This part of the documentation covers all the interfaces of Flask. For parts where Flask depends on external libraries, we document the most important right here and provide links to the canonical documentation.
Application Object
class flask.Flask(import_name, static_url_path=None, static_folder='static', static_host=None, host_matching=False, subdomain_matching=False, template_folder='templates', instance_path=None, instance_relative_config=False, root_path=None)
The flask object implements a WSGI application and acts as the central object. It is passed the name of the module or package of the application. Once it is created it will act as a central registry for the view functions, the URL rules, template configuration and much more.
The name of the package is used to resolve resources from inside the
package or the folder the module is contained in depending on if the
package parameter resolves to an actual python package (a folder with
an __init__.py file inside) or a standard module (just a .py file).
For more information about resource loading, see open_resource().
Usually you create a Flask instance in your main module or
in the __init__.py file of your package like this:
from flask import Flask
app = Flask(__name__)
About the First Parameter
The idea of the first parameter is to give Flask an idea of what belongs to your application. This name is used to find resources on the filesystem, can be used by extensions to improve debugging information and a lot more.
So it’s important what you provide there. If you are using a single module, [UNKNOWN NODE title_reference] is always the correct value. If you however are using a package, it’s usually recommended to hardcode the name of your package there.
For example if your application is defined in yourapplication/app.py
you should create it with one of the two versions below:
app = Flask('yourapplication')
app = Flask(__name__.split('.')[0])
Why is that? The application will work even with [UNKNOWN NODE title_reference], thanks to how resources are looked up. However it will make debugging more painful. Certain extensions can make assumptions based on the import name of your application. For example the Flask-SQLAlchemy extension will look for the code in your application that triggered an SQL query in debug mode. If the import name is not properly set up, that debugging information is lost. (For example it would only pick up SQL queries in [UNKNOWN NODE title_reference] and not [UNKNOWN NODE title_reference])
New in version 0.7: The [UNKNOWN NODE title_reference], [UNKNOWN NODE title_reference], and [UNKNOWN NODE title_reference] parameters were added.
New in version 0.8: The [UNKNOWN NODE title_reference] and [UNKNOWN NODE title_reference] parameters were added.
New in version 0.11: The [UNKNOWN NODE title_reference] parameter was added.
New in version 1.0: The host_matching and static_host parameters were added.
New in version 1.0: The subdomain_matching parameter was added. Subdomain
matching needs to be enabled manually now. Setting
SERVER_NAME does not implicitly enable it.
- import_name – the name of the application package
- static_url_path – can be used to specify a different path for the static files on the web. Defaults to the name of the [UNKNOWN NODE title_reference] folder.
- static_folder – the folder with static files that should be served
at [UNKNOWN NODE title_reference]. Defaults to the
'static'folder in the root path of the application. - static_host – the host to use when adding the static route.
Defaults to None. Required when using
host_matching=Truewith astatic_folderconfigured. - host_matching – set
url_map.host_matchingattribute. Defaults to False. - subdomain_matching – consider the subdomain relative to
SERVER_NAMEwhen matching routes. Defaults to False. - template_folder – the folder that contains the templates that should
be used by the application. Defaults to
'templates'folder in the root path of the application. - instance_path – An alternative instance path for the application.
By default the folder
'instance'next to the package or module is assumed to be the instance path. - instance_relative_config – if set to
Truerelative filenames for loading the config are assumed to be relative to the instance path instead of the application root. - root_path – Flask by default will automatically calculate the path to the root of the application. In certain situations this cannot be achieved (for instance if the package is a Python 3 namespace package) and needs to be manually defined.
add_template_filter(f, name=None)
Register a custom template filter. Works exactly like the
template_filter() decorator.
add_template_global(f, name=None)
Register a custom template global function. Works exactly like the
template_global() decorator.
New in version 0.10.
add_template_test(f, name=None)
Register a custom template test. Works exactly like the
template_test() decorator.
New in version 0.10.
add_url_rule(rule, endpoint=None, view_func=None, provide_automatic_options=None, **options)
Connects a URL rule. Works exactly like the route()
decorator. If a view_func is provided it will be registered with the
endpoint.
Basically this example:
@app.route('/')
def index():
pass
Is equivalent to the following:
def index():
pass
app.add_url_rule('/', 'index', index)
If the view_func is not provided you will need to connect the endpoint to a view function like so:
app.view_functions['index'] = index
Internally route() invokes add_url_rule() so if you want
to customize the behavior via subclassing you only need to change
this method.
For more information refer to URL Route Registrations.
Changed in version 0.2: [UNKNOWN NODE title_reference] parameter added.
Changed in version 0.6: OPTIONS is added automatically as method.
- rule – the URL rule as string
- endpoint – the endpoint for the registered URL rule. Flask itself assumes the name of the view function as endpoint
- view_func – the function to call when serving a request to the provided endpoint
- provide_automatic_options – controls whether the
OPTIONSmethod should be added automatically. This can also be controlled by setting theview_func.provide_automatic_options = Falsebefore adding the rule. - options – the options to be forwarded to the underlying
Ruleobject. A change to Werkzeug is handling of method options. methods is a list of methods this rule should be limited to (GET,POSTetc.). By default a rule just listens forGET(and implicitlyHEAD). Starting with Flask 0.6,OPTIONSis implicitly added and handled by the standard request handling.
after_request(f)
Register a function to be run after each request.
Your function must take one parameter, an instance of
response_class and return a new response object or the
same (see process_response()).
As of Flask 0.7 this function might not be executed at the end of the request in case an unhandled exception occurred.
after_request_funcs = None
A dictionary with lists of functions that should be called after
each request. The key of the dictionary is the name of the blueprint
this function is active for, None for all requests. This can for
example be used to close database connections. To register a function
here, use the after_request() decorator.
app_context()
Binds the application only. For as long as the application is bound
to the current context the flask.current_app points to that
application. An application context is automatically created when a
request context is pushed if necessary.
Example usage:
with app.app_context():
...
New in version 0.9.
app_ctx_globals_class
alias of flask.ctx._AppCtxGlobals
auto_find_instance_path()
Tries to locate the instance path if it was not provided to the
constructor of the application class. It will basically calculate
the path to a folder named instance next to your main file or
the package.
New in version 0.8.
before_first_request(f)
Registers a function to be run before the first request to this instance of the application.
The function will be called without any arguments and its return value is ignored.
New in version 0.8.
before_first_request_funcs = None
A list of functions that will be called at the beginning of the
first request to this instance. To register a function, use the
before_first_request() decorator.
New in version 0.8.
before_request(f)
Registers a function to run before each request.
For example, this can be used to open a database connection, or to load the logged in user from the session.
The function will be called without any arguments. If it returns a non-None value, the value is handled as if it was the return value from the view, and further request handling is stopped.
before_request_funcs = None
A dictionary with lists of functions that will be called at the
beginning of each request. The key of the dictionary is the name of
the blueprint this function is active for, or None for all
requests. To register a function, use the before_request()
decorator.
blueprints = None
all the attached blueprints in a dictionary by name. Blueprints can be attached multiple times so this dictionary does not tell you how often they got attached.
New in version 0.7.
cli = None
The click command line context for this application. Commands registered here show up in the flask command once the application has been discovered. The default commands are provided by Flask itself and can be overridden.
This is an instance of a click.Group object.
config = None
The configuration dictionary as Config. This behaves
exactly like a regular dictionary but supports additional methods
to load a config from files.
config_class
alias of flask.config.Config
context_processor(f)
Registers a template context processor function.
create_global_jinja_loader()
Creates the loader for the Jinja2 environment. Can be used to
override just the loader and keeping the rest unchanged. It’s
discouraged to override this function. Instead one should override
the jinja_loader() function instead.
The global loader dispatches between the loaders of the application and the individual blueprints.
New in version 0.7.
create_jinja_environment()
Creates the Jinja2 environment based on jinja_options
and select_jinja_autoescape(). Since 0.7 this also adds
the Jinja2 globals and filters after initialization. Override
this function to customize the behavior.
New in version 0.5.
Changed in version 0.11: Environment.auto_reload set in accordance with
TEMPLATES_AUTO_RELOAD configuration option.
create_url_adapter(request)
Creates a URL adapter for the given request. The URL adapter is created at a point where the request context is not yet set up so the request is passed explicitly.
New in version 0.6.
Changed in version 0.9: This can now also be called without a request object when the URL adapter is created for the application context.
Changed in version 1.0: SERVER_NAME no longer implicitly enables subdomain
matching. Use subdomain_matching instead.
debug
Whether debug mode is enabled. When using flask run to start
the development server, an interactive debugger will be shown for
unhandled exceptions, and the server will be reloaded when code
changes. This maps to the DEBUG config key. This is
enabled when env is 'development' and is overridden
by the FLASK_DEBUG environment variable. It may not behave as
expected if set in code.
Do not enable debug mode when deploying in production.
Default: True if env is 'development', or
False otherwise.
default_config = {'APPLICATION_ROOT': '/', 'DEBUG': None, 'ENV': None, 'EXPLAIN_TEMPLATE_LOADING': False, 'JSONIFY_MIMETYPE': 'application/json', 'JSONIFY_PRETTYPRINT_REGULAR': False, 'JSON_AS_ASCII': True, 'JSON_SORT_KEYS': True, 'MAX_CONTENT_LENGTH': None, 'PERMANENT_SESSION_LIFETIME': datetime.timedelta(31), 'PREFERRED_URL_SCHEME': 'http', 'PRESERVE_CONTEXT_ON_EXCEPTION': None, 'PROPAGATE_EXCEPTIONS': None, 'SECRET_KEY': None, 'SEND_FILE_MAX_AGE_DEFAULT': datetime.timedelta(0, 43200), 'SERVER_NAME': None, 'SESSION_COOKIE_DOMAIN': None, 'SESSION_COOKIE_HTTPONLY': True, 'SESSION_COOKIE_NAME': 'session', 'SESSION_COOKIE_PATH': None, 'SESSION_COOKIE_SAMESITE': None, 'SESSION_COOKIE_SECURE': False, 'SESSION_REFRESH_EACH_REQUEST': True, 'TEMPLATES_AUTO_RELOAD': None, 'TESTING': False, 'TRAP_BAD_REQUEST_ERRORS': None, 'TRAP_HTTP_EXCEPTIONS': False, 'USE_X_SENDFILE': False}
Default configuration parameters.
dispatch_request()
Does the request dispatching. Matches the URL and returns the
return value of the view or error handler. This does not have to
be a response object. In order to convert the return value to a
proper response object, call make_response().
Changed in version 0.7: This no longer does the exception handling, this code was
moved to the new full_dispatch_request().
do_teardown_appcontext(exc=<object object>)
Called when an application context is popped. This works pretty
much the same as do_teardown_request() but for the application
context.
New in version 0.9.
do_teardown_request(exc=<object object>)
Called after the actual request dispatching and will
call every as teardown_request() decorated function. This is
not actually called by the Flask object itself but is always
triggered when the request context is popped. That way we have a
tighter control over certain resources under testing environments.
Changed in version 0.9: Added the [UNKNOWN NODE title_reference] argument. Previously this was always using the current exception information.
endpoint(endpoint)
A decorator to register a function as an endpoint. Example:
@app.endpoint('example.endpoint')
def example():
return "example"
env
What environment the app is running in. Flask and extensions may
enable behaviors based on the environment, such as enabling debug
mode. This maps to the ENV config key. This is set by the
FLASK_ENV environment variable and may not behave as
expected if set in code.
Do not enable development when deploying in production.
Default: 'production'
error_handler_spec = None
A dictionary of all registered error handlers. The key is None
for error handlers active on the application, otherwise the key is
the name of the blueprint. Each key points to another dictionary
where the key is the status code of the http exception. The
special key None points to a list of tuples where the first item
is the class for the instance check and the second the error handler
function.
To register an error handler, use the errorhandler()
decorator.
errorhandler(code_or_exception)
Register a function to handle errors by code or exception class.
A decorator that is used to register a function given an error code. Example:
@app.errorhandler(404)
def page_not_found(error):
return 'This page does not exist', 404
You can also register handlers for arbitrary exceptions:
@app.errorhandler(DatabaseError)
def special_exception_handler(error):
return 'Database connection failed', 500
New in version 0.7: Use register_error_handler() instead of modifying
error_handler_spec directly, for application wide error
handlers.
New in version 0.7: One can now additionally also register custom exception types
that do not necessarily have to be a subclass of the
HTTPException class.
extensions = None
a place where extensions can store application specific state. For example this is where an extension could store database engines and similar things. For backwards compatibility extensions should register themselves like this:
if not hasattr(app, 'extensions'):
app.extensions = {}
app.extensions['extensionname'] = SomeObject()
The key must match the name of the extension module. For example in
case of a “Flask-Foo” extension in [UNKNOWN NODE title_reference], the key would be
'foo'.
New in version 0.7.
full_dispatch_request()
Dispatches the request and on top of that performs request pre and postprocessing as well as HTTP exception catching and error handling.
New in version 0.7.
get_send_file_max_age(filename)
Provides default cache_timeout for the send_file() functions.
By default, this function returns SEND_FILE_MAX_AGE_DEFAULT from
the configuration of current_app.
Static file functions such as send_from_directory() use this
function, and send_file() calls this function on
current_app when the given cache_timeout is None. If a
cache_timeout is given in send_file(), that timeout is used;
otherwise, this method is called.
This allows subclasses to change the behavior when sending files based on the filename. For example, to set the cache timeout for .js files to 60 seconds:
class MyFlask(flask.Flask):
def get_send_file_max_age(self, name):
if name.lower().endswith('.js'):
return 60
return flask.Flask.get_send_file_max_age(self, name)
New in version 0.9.
got_first_request
This attribute is set to True if the application started
handling the first request.
New in version 0.8.
handle_exception(e)
Default exception handling that kicks in when an exception occurs that is not caught. In debug mode the exception will be re-raised immediately, otherwise it is logged and the handler for a 500 internal server error is used. If no such handler exists, a default 500 internal server error message is displayed.
New in version 0.3.
handle_http_exception(e)
Handles an HTTP exception. By default this will invoke the registered error handlers and fall back to returning the exception as response.
New in version 0.3.
handle_url_build_error(error, endpoint, values)
Handle BuildError on url_for().
handle_user_exception(e)
This method is called whenever an exception occurs that should be
handled. A special case are
HTTPExceptions which are forwarded by
this function to the handle_http_exception() method. This
function will either return a response value or reraise the
exception with the same traceback.
Changed in version 1.0: Key errors raised from request data like form show the the bad
key in debug mode rather than a generic bad request message.
New in version 0.7.
has_static_folder
This is True if the package bound object’s container has a
folder for static files.
New in version 0.5.
import_name = None
The name of the package or module that this app belongs to. Do not change this once it is set by the constructor.
inject_url_defaults(endpoint, values)
Injects the URL defaults for the given endpoint directly into the values dictionary passed. This is used internally and automatically called on URL building.
New in version 0.7.
instance_path = None
Holds the path to the instance folder.
New in version 0.8.
iter_blueprints()
Iterates over all blueprints by the order they were registered.
New in version 0.11.
jinja_env
The Jinja2 environment used to load templates.
jinja_environment
alias of flask.templating.Environment
jinja_loader
The Jinja loader for this package bound object.
New in version 0.5.
jinja_options = {'extensions': ['jinja2.ext.autoescape', 'jinja2.ext.with_']}
Options that are passed directly to the Jinja2 environment.
json_decoder
alias of flask.json.JSONDecoder
json_encoder
alias of flask.json.JSONEncoder
log_exception(exc_info)
Logs an exception. This is called by handle_exception()
if debugging is disabled and right before the handler is called.
The default implementation logs the exception as error on the
logger.
New in version 0.8.
logger
The 'flask.app' logger, a standard Python
Logger.
In debug mode, the logger’s level will be set
to DEBUG.
If there are no handlers configured, a default handler will be added. See Logging for more information.
Changed in version 1.0: Behavior was simplified. The logger is always named
flask.app. The level is only set during configuration, it
doesn’t check app.debug each time. Only one format is used,
not different ones depending on app.debug. No handlers are
removed, and a handler is only added if no handlers are already
configured.
New in version 0.3.
make_config(instance_relative=False)
Used to create the config attribute by the Flask constructor. The [UNKNOWN NODE title_reference] parameter is passed in from the constructor of Flask (there named [UNKNOWN NODE title_reference]) and indicates if the config should be relative to the instance path or the root path of the application.
New in version 0.8.
make_default_options_response()
This method is called to create the default OPTIONS response.
This can be changed through subclassing to change the default
behavior of OPTIONS responses.
New in version 0.7.
make_null_session()
Creates a new instance of a missing session. Instead of overriding
this method we recommend replacing the session_interface.
New in version 0.7.
make_response(rv)
Convert the return value from a view function to an instance of
response_class.
the return value from the view function. The view function
must return a response. Returning None, or the view ending
without returning, is not allowed. The following types are allowed
for view_rv:
str(unicodein Python 2)- A response object is created with the string encoded to UTF-8 as the body.
bytes(strin Python 2)- A response object is created with the bytes as the body.
tuple- Either
(body, status, headers),(body, status), or(body, headers), wherebodyis any of the other types allowed here,statusis a string or an integer, andheadersis a dictionary or a list of(key, value)tuples. Ifbodyis aresponse_classinstance,statusoverwrites the exiting value andheadersare extended. response_class- The object is returned unchanged.
- other
Responseclass - The object is coerced to
response_class. callable()- The function is called as a WSGI application. The result is used to create a response object.
Changed in version 0.9: Previously a tuple was interpreted as the arguments for the response object.
make_shell_context()
Returns the shell context for an interactive shell for this application. This runs all the registered shell context processors.
New in version 0.11.
name
The name of the application. This is usually the import name with the difference that it’s guessed from the run file if the import name is main. This name is used as a display name when Flask needs the name of the application. It can be set and overridden to change the value.
New in version 0.8.
open_instance_resource(resource, mode='rb')
Opens a resource from the application’s instance folder
(instance_path). Otherwise works like
open_resource(). Instance resources can also be opened for
writing.
- resource – the name of the resource. To access resources within subfolders use forward slashes as separator.
- mode – resource file opening mode, default is ‘rb’.
open_resource(resource, mode='rb')
Opens a resource from the application’s resource folder. To see how this works, consider the following folder structure:
/myapplication.py
/schema.sql
/static
/style.css
/templates
/layout.html
/index.html
If you want to open the schema.sql file you would do the
following:
with app.open_resource('schema.sql') as f:
contents = f.read()
do_something_with(contents)
- resource – the name of the resource. To access resources within subfolders use forward slashes as separator.
- mode – resource file opening mode, default is ‘rb’.
open_session(request)
Creates or opens a new session. Default implementation stores all
session data in a signed cookie. This requires that the
secret_key is set. Instead of overriding this method
we recommend replacing the session_interface.
request_class.permanent_session_lifetime
A timedelta which is used to set the expiration
date of a permanent session. The default is 31 days which makes a
permanent session survive for roughly one month.
This attribute can also be configured from the config with the
PERMANENT_SESSION_LIFETIME configuration key. Defaults to
timedelta(days=31)
preprocess_request()
Called before the request is dispatched. Calls
url_value_preprocessors registered with the app and the
current blueprint (if any). Then calls before_request_funcs
registered with the app and the blueprint.
If any before_request() handler returns a non-None value, the
value is handled as if it was the return value from the view, and
further request handling is stopped.
preserve_context_on_exception
Returns the value of the PRESERVE_CONTEXT_ON_EXCEPTION
configuration value in case it’s set, otherwise a sensible default
is returned.
New in version 0.7.
process_response(response)
Can be overridden in order to modify the response object
before it’s sent to the WSGI server. By default this will
call all the after_request() decorated functions.
Changed in version 0.5: As of Flask 0.5 the functions registered for after request execution are called in reverse order of registration.
response_class object.response_class.propagate_exceptions
Returns the value of the PROPAGATE_EXCEPTIONS configuration
value in case it’s set, otherwise a sensible default is returned.
New in version 0.7.
register_blueprint(blueprint, **options)
Register a Blueprint on the application. Keyword
arguments passed to this method will override the defaults set on the
blueprint.
Calls the blueprint’s register() method after
recording the blueprint in the application’s blueprints.
- blueprint – The blueprint to register.
- url_prefix – Blueprint routes will be prefixed with this.
- subdomain – Blueprint routes will match on this subdomain.
- url_defaults – Blueprint routes will use these default values for view arguments.
- options – Additional keyword arguments are passed to
BlueprintSetupState. They can be accessed inrecord()callbacks.
New in version 0.7.
register_error_handler(code_or_exception, f)
Alternative error attach function to the errorhandler()
decorator that is more straightforward to use for non decorator
usage.
New in version 0.7.
request_class
alias of flask.wrappers.Request
request_context(environ)
Creates a RequestContext from the given
environment and binds it to the current context. This must be used in
combination with the with statement because the request is only bound
to the current context for the duration of the with block.
Example usage:
with app.request_context(environ):
do_something_with(request)
The object returned can also be used without the with statement
which is useful for working in the shell. The example above is
doing exactly the same as this code:
ctx = app.request_context(environ)
ctx.push()
try:
do_something_with(request)
finally:
ctx.pop()
Changed in version 0.3: Added support for non-with statement usage and with statement
is now passed the ctx object.
response_class
alias of flask.wrappers.Response
root_path = None
Absolute path to the package on the filesystem. Used to look up resources contained in the package.
route(rule, **options)
A decorator that is used to register a view function for a
given URL rule. This does the same thing as add_url_rule()
but is intended for decorator usage:
@app.route('/')
def index():
return 'Hello World'
For more information refer to URL Route Registrations.
- rule – the URL rule as string
- endpoint – the endpoint for the registered URL rule. Flask itself assumes the name of the view function as endpoint
- options – the options to be forwarded to the underlying
Ruleobject. A change to Werkzeug is handling of method options. methods is a list of methods this rule should be limited to (GET,POSTetc.). By default a rule just listens forGET(and implicitlyHEAD). Starting with Flask 0.6,OPTIONSis implicitly added and handled by the standard request handling.
run(host=None, port=None, debug=None, load_dotenv=True, **options)
Runs the application on a local development server.
Do not use run() in a production setting. It is not intended to
meet security and performance requirements for a production server.
Instead, see Deployment Options for WSGI server recommendations.
If the debug flag is set the server will automatically reload
for code changes and show a debugger in case an exception happened.
If you want to run the application in debug mode, but disable the
code execution on the interactive debugger, you can pass
use_evalex=False as parameter. This will keep the debugger’s
traceback screen active, but disable code execution.
It is not recommended to use this function for development with
automatic reloading as this is badly supported. Instead you should
be using the flask command line script’s run support.
Keep in Mind
Flask will suppress any server error with a generic error page
unless it is in debug mode. As such to enable just the
interactive debugger without the code reloading, you have to
invoke run() with debug=True and use_reloader=False.
Setting use_debugger to True without being in debug mode
won’t catch any exceptions because there won’t be any to
catch.
- host – the hostname to listen on. Set this to
'0.0.0.0'to have the server available externally as well. Defaults to'127.0.0.1'or the host in theSERVER_NAMEconfig variable if present. - port – the port of the webserver. Defaults to
5000or the port defined in theSERVER_NAMEconfig variable if present. - debug – if given, enable or disable debug mode. See
debug. - load_dotenv – Load the nearest
.envand.flaskenvfiles to set environment variables. Will also change the working directory to the directory containing the first file found. - options – the options to be forwarded to the underlying Werkzeug
server. See
werkzeug.serving.run_simple()for more information.
Changed in version 1.0: If installed, python-dotenv will be used to load environment
variables from .env and .flaskenv files.
If set, the FLASK_ENV and FLASK_DEBUG
environment variables will override env and
debug.
Threaded mode is enabled by default.
Changed in version 0.10: The default port is now picked from the SERVER_NAME
variable.
save_session(session, response)
Saves the session if it needs updates. For the default
implementation, check open_session(). Instead of overriding this
method we recommend replacing the session_interface.
- session – the session to be saved (a
SecureCookieobject) - response – an instance of
response_class
secret_key
If a secret key is set, cryptographic components can use this to sign cookies and other things. Set this to a complex random value when you want to use the secure cookie for instance.
This attribute can also be configured from the config with the
SECRET_KEY configuration key. Defaults to None.
select_jinja_autoescape(filename)
Returns True if autoescaping should be active for the given
template name. If no template name is given, returns [UNKNOWN NODE title_reference].
New in version 0.5.
send_file_max_age_default
A timedelta which is used as default cache_timeout
for the send_file() functions. The default is 12 hours.
This attribute can also be configured from the config with the
SEND_FILE_MAX_AGE_DEFAULT configuration key. This configuration
variable can also be set with an integer value used as seconds.
Defaults to timedelta(hours=12)
send_static_file(filename)
Function used internally to send static files from the static folder to the browser.
New in version 0.5.
session_cookie_name
The secure cookie uses this for the name of the session cookie.
This attribute can also be configured from the config with the
SESSION_COOKIE_NAME configuration key. Defaults to 'session'
session_interface = <flask.sessions.SecureCookieSessionInterface object>
the session interface to use. By default an instance of
SecureCookieSessionInterface is used here.
New in version 0.8.
shell_context_processor(f)
Registers a shell context processor function.
New in version 0.11.
shell_context_processors = None
A list of shell context processor functions that should be run when a shell context is created.
New in version 0.11.
should_ignore_error(error)
This is called to figure out if an error should be ignored
or not as far as the teardown system is concerned. If this
function returns True then the teardown handlers will not be
passed the error.
New in version 0.10.
static_folder
The absolute path to the configured static folder.
static_url_path
The URL prefix that the static route will be registered for.
teardown_appcontext(f)
Registers a function to be called when the application context ends. These functions are typically also called when the request context is popped.
Example:
ctx = app.app_context()
ctx.push()
...
ctx.pop()
When ctx.pop() is executed in the above example, the teardown
functions are called just before the app context moves from the
stack of active contexts. This becomes relevant if you are using
such constructs in tests.
Since a request context typically also manages an application context it would also be called when you pop a request context.
When a teardown function was called because of an unhandled exception
it will be passed an error object. If an errorhandler() is
registered, it will handle the exception and the teardown will not
receive it.
The return values of teardown functions are ignored.
New in version 0.9.
teardown_appcontext_funcs = None
A list of functions that are called when the application context is destroyed. Since the application context is also torn down if the request ends this is the place to store code that disconnects from databases.
New in version 0.9.
teardown_request(f)
Register a function to be run at the end of each request, regardless of whether there was an exception or not. These functions are executed when the request context is popped, even if not an actual request was performed.
Example:
ctx = app.test_request_context()
ctx.push()
...
ctx.pop()
When ctx.pop() is executed in the above example, the teardown
functions are called just before the request context moves from the
stack of active contexts. This becomes relevant if you are using
such constructs in tests.
Generally teardown functions must take every necessary step to avoid that they will fail. If they do execute code that might fail they will have to surround the execution of these code by try/except statements and log occurring errors.
When a teardown function was called because of an exception it will be passed an error object.
The return values of teardown functions are ignored.
Debug Note
In debug mode Flask will not tear down a request on an exception
immediately. Instead it will keep it alive so that the interactive
debugger can still access it. This behavior can be controlled
by the PRESERVE_CONTEXT_ON_EXCEPTION configuration variable.
teardown_request_funcs = None
A dictionary with lists of functions that are called after
each request, even if an exception has occurred. The key of the
dictionary is the name of the blueprint this function is active for,
None for all requests. These functions are not allowed to modify
the request, and their return values are ignored. If an exception
occurred while processing the request, it gets passed to each
teardown_request function. To register a function here, use the
teardown_request() decorator.
New in version 0.7.
template_context_processors = None
A dictionary with list of functions that are called without argument
to populate the template context. The key of the dictionary is the
name of the blueprint this function is active for, None for all
requests. Each returns a dictionary that the template context is
updated with. To register a function here, use the
context_processor() decorator.
template_filter(name=None)
A decorator that is used to register custom template filter. You can specify a name for the filter, otherwise the function name will be used. Example:
@app.template_filter()
def reverse(s):
return s[::-1]
template_folder = None
Location of the template files to be added to the template lookup.
None if templates should not be added.
template_global(name=None)
A decorator that is used to register a custom template global function. You can specify a name for the global function, otherwise the function name will be used. Example:
@app.template_global()
def double(n):
return 2 * n
New in version 0.10.
template_test(name=None)
A decorator that is used to register custom template test. You can specify a name for the test, otherwise the function name will be used. Example:
@app.template_test()
def is_prime(n):
if n == 2:
return True
for i in range(2, int(math.ceil(math.sqrt(n))) + 1):
if n % i == 0:
return False
return True
New in version 0.10.
templates_auto_reload
Reload templates when they are changed. Used by
create_jinja_environment().
This attribute can be configured with TEMPLATES_AUTO_RELOAD. If
not set, it will be enabled in debug mode.
New in version 1.0: This property was added but the underlying config and behavior already existed.
test_cli_runner(**kwargs)
Create a CLI runner for testing CLI commands. See Testing CLI Commands.
Returns an instance of test_cli_runner_class, by default
FlaskCliRunner. The Flask app object is
passed as the first argument.
New in version 1.0.
test_cli_runner_class = None
The CliRunner subclass, by default
FlaskCliRunner that is used by
test_cli_runner(). Its __init__ method should take a
Flask app object as the first argument.
New in version 1.0.
test_client(use_cookies=True, **kwargs)
Creates a test client for this application. For information about unit testing head over to Testing Flask Applications.
Note that if you are testing for assertions or exceptions in your
application code, you must set app.testing = True in order for the
exceptions to propagate to the test client. Otherwise, the exception
will be handled by the application (not visible to the test client) and
the only indication of an AssertionError or other exception will be a
500 status code response to the test client. See the testing
attribute. For example:
app.testing = True
client = app.test_client()
The test client can be used in a with block to defer the closing down
of the context until the end of the with block. This is useful if
you want to access the context locals for testing:
with app.test_client() as c:
rv = c.get('/?vodka=42')
assert request.args['vodka'] == '42'
Additionally, you may pass optional keyword arguments that will then
be passed to the application’s test_client_class constructor.
For example:
from flask.testing import FlaskClient
class CustomClient(FlaskClient):
def __init__(self, *args, **kwargs):
self._authentication = kwargs.pop("authentication")
super(CustomClient,self).__init__( *args, **kwargs)
app.test_client_class = CustomClient
client = app.test_client(authentication='Basic ....')
See FlaskClient for more information.
Changed in version 0.4: added support for with block usage for the client.
New in version 0.7: The [UNKNOWN NODE title_reference] parameter was added as well as the ability
to override the client to be used by setting the
test_client_class attribute.
Changed in version 0.11: Added [UNKNOWN NODE title_reference] to support passing additional keyword arguments to
the constructor of test_client_class.
test_client_class = None
the test client that is used with when [UNKNOWN NODE title_reference] is used.
New in version 0.7.
test_request_context(*args, **kwargs)
Creates a RequestContext from the given values
(see werkzeug.test.EnvironBuilder for more information, this
function accepts the same arguments plus two additional).
Additional arguments (only if base_url is not specified):
- subdomain – subdomain to use for route matching
- url_scheme – scheme for the request, default
PREFERRED_URL_SCHEMEorhttp.
testing
The testing flag. Set this to True to enable the test mode of
Flask extensions (and in the future probably also Flask itself).
For example this might activate test helpers that have an
additional runtime cost which should not be enabled by default.
If this is enabled and PROPAGATE_EXCEPTIONS is not changed from the default it’s implicitly enabled.
This attribute can also be configured from the config with the
TESTING configuration key. Defaults to False.
trap_http_exception(e)
Checks if an HTTP exception should be trapped or not. By default
this will return False for all exceptions except for a bad request
key error if TRAP_BAD_REQUEST_ERRORS is set to True. It
also returns True if TRAP_HTTP_EXCEPTIONS is set to True.
This is called for all HTTP exceptions raised by a view function.
If it returns True for any exception the error handler for this
exception is not called and it shows up as regular exception in the
traceback. This is helpful for debugging implicitly raised HTTP
exceptions.
Changed in version 1.0: Bad request errors are not trapped by default in debug mode.
New in version 0.8.
update_template_context(context)
Update the template context with some commonly used variables. This injects request, session, config and g into the template context as well as everything template context processors want to inject. Note that the as of Flask 0.6, the original values in the context will not be overridden if a context processor decides to return a value with the same key.
url_build_error_handlers = None
A list of functions that are called when url_for() raises a
BuildError. Each function registered here
is called with [UNKNOWN NODE title_reference], [UNKNOWN NODE title_reference] and [UNKNOWN NODE title_reference]. If a function
returns None or raises a BuildError the next function is
tried.
New in version 0.9.
url_default_functions = None
A dictionary with lists of functions that can be used as URL value
preprocessors. The key None here is used for application wide
callbacks, otherwise the key is the name of the blueprint.
Each of these functions has the chance to modify the dictionary
of URL values before they are used as the keyword arguments of the
view function. For each function registered this one should also
provide a url_defaults() function that adds the parameters
automatically again that were removed that way.
New in version 0.7.
url_defaults(f)
Callback function for URL defaults for all view functions of the application. It’s called with the endpoint and values and should update the values passed in place.
url_map = None
The Map for this instance. You can use
this to change the routing converters after the class was created
but before any routes are connected. Example:
from werkzeug.routing import BaseConverter
class ListConverter(BaseConverter):
def to_python(self, value):
return value.split(',')
def to_url(self, values):
return ','.join(super(ListConverter, self).to_url(value)
for value in values)
app = Flask(__name__)
app.url_map.converters['list'] = ListConverter
url_rule_class
alias of werkzeug.routing.Rule
url_value_preprocessor(f)
Register a URL value preprocessor function for all view
functions in the application. These functions will be called before the
before_request() functions.
The function can modify the values captured from the matched url before
they are passed to the view. For example, this can be used to pop a
common language code value and place it in g rather than pass it to
every view.
The function is passed the endpoint name and values dict. The return value is ignored.
url_value_preprocessors = None
A dictionary with lists of functions that are called before the
before_request_funcs functions. The key of the dictionary is
the name of the blueprint this function is active for, or None
for all requests. To register a function, use
url_value_preprocessor().
New in version 0.7.
use_x_sendfile
Enable this if you want to use the X-Sendfile feature. Keep in
mind that the server has to support this. This only affects files
sent with the send_file() method.
New in version 0.2.
This attribute can also be configured from the config with the
USE_X_SENDFILE configuration key. Defaults to False.
view_functions = None
A dictionary of all view functions registered. The keys will
be function names which are also used to generate URLs and
the values are the function objects themselves.
To register a view function, use the route() decorator.
wsgi_app(environ, start_response)
The actual WSGI application. This is not implemented in [UNKNOWN NODE title_reference] so that middlewares can be applied without losing a reference to the class. So instead of doing this:
app = MyMiddleware(app)
It’s a better idea to do this instead:
app.wsgi_app = MyMiddleware(app.wsgi_app)
Then you still have the original application object around and can continue to call methods on it.
Changed in version 0.7: The behavior of the before and after request callbacks was changed under error conditions and a new callback was added that will always execute at the end of the request, independent on if an error occurred or not. See Callbacks and Errors.
- environ – a WSGI environment
- start_response – a callable accepting a status code, a list of headers and an optional exception context to start the response
Blueprint Objects
class flask.Blueprint(name, import_name, static_folder=None, static_url_path=None, template_folder=None, url_prefix=None, subdomain=None, url_defaults=None, root_path=None)
Represents a blueprint. A blueprint is an object that records
functions that will be called with the
BlueprintSetupState later to register functions
or other things on the main application. See Modular Applications with Blueprints for more
information.
New in version 0.7.
add_app_template_filter(f, name=None)
Register a custom template filter, available application wide. Like
Flask.add_template_filter() but for a blueprint. Works exactly
like the app_template_filter() decorator.
add_app_template_global(f, name=None)
Register a custom template global, available application wide. Like
Flask.add_template_global() but for a blueprint. Works exactly
like the app_template_global() decorator.
New in version 0.10.
add_app_template_test(f, name=None)
Register a custom template test, available application wide. Like
Flask.add_template_test() but for a blueprint. Works exactly
like the app_template_test() decorator.
New in version 0.10.
add_url_rule(rule, endpoint=None, view_func=None, **options)
Like Flask.add_url_rule() but for a blueprint. The endpoint for
the url_for() function is prefixed with the name of the blueprint.
after_app_request(f)
Like Flask.after_request() but for a blueprint. Such a function
is executed after each request, even if outside of the blueprint.
after_request(f)
Like Flask.after_request() but for a blueprint. This function
is only executed after each request that is handled by a function of
that blueprint.
app_context_processor(f)
Like Flask.context_processor() but for a blueprint. Such a
function is executed each request, even if outside of the blueprint.
app_errorhandler(code)
Like Flask.errorhandler() but for a blueprint. This
handler is used for all requests, even if outside of the blueprint.
app_template_filter(name=None)
Register a custom template filter, available application wide. Like
Flask.template_filter() but for a blueprint.
app_template_global(name=None)
Register a custom template global, available application wide. Like
Flask.template_global() but for a blueprint.
New in version 0.10.
app_template_test(name=None)
Register a custom template test, available application wide. Like
Flask.template_test() but for a blueprint.
New in version 0.10.
app_url_defaults(f)
Same as url_defaults() but application wide.
app_url_value_preprocessor(f)
Same as url_value_preprocessor() but application wide.
before_app_first_request(f)
Like Flask.before_first_request(). Such a function is
executed before the first request to the application.
before_app_request(f)
Like Flask.before_request(). Such a function is executed
before each request, even if outside of a blueprint.
before_request(f)
Like Flask.before_request() but for a blueprint. This function
is only executed before each request that is handled by a function of
that blueprint.
context_processor(f)
Like Flask.context_processor() but for a blueprint. This
function is only executed for requests handled by a blueprint.
endpoint(endpoint)
Like Flask.endpoint() but for a blueprint. This does not
prefix the endpoint with the blueprint name, this has to be done
explicitly by the user of this method. If the endpoint is prefixed
with a [UNKNOWN NODE title_reference] it will be registered to the current blueprint, otherwise
it’s an application independent endpoint.
errorhandler(code_or_exception)
Registers an error handler that becomes active for this blueprint only. Please be aware that routing does not happen local to a blueprint so an error handler for 404 usually is not handled by a blueprint unless it is caused inside a view function. Another special case is the 500 internal server error which is always looked up from the application.
Otherwise works as the errorhandler() decorator
of the Flask object.
get_send_file_max_age(filename)
Provides default cache_timeout for the send_file() functions.
By default, this function returns SEND_FILE_MAX_AGE_DEFAULT from
the configuration of current_app.
Static file functions such as send_from_directory() use this
function, and send_file() calls this function on
current_app when the given cache_timeout is None. If a
cache_timeout is given in send_file(), that timeout is used;
otherwise, this method is called.
This allows subclasses to change the behavior when sending files based on the filename. For example, to set the cache timeout for .js files to 60 seconds:
class MyFlask(flask.Flask):
def get_send_file_max_age(self, name):
if name.lower().endswith('.js'):
return 60
return flask.Flask.get_send_file_max_age(self, name)
New in version 0.9.
has_static_folder
This is True if the package bound object’s container has a
folder for static files.
New in version 0.5.
import_name = None
The name of the package or module that this app belongs to. Do not change this once it is set by the constructor.
jinja_loader
The Jinja loader for this package bound object.
New in version 0.5.
json_decoder = None
Blueprint local JSON decoder class to use.
Set to None to use the app’s json_decoder.
json_encoder = None
Blueprint local JSON decoder class to use.
Set to None to use the app’s json_encoder.
make_setup_state(app, options, first_registration=False)
Creates an instance of BlueprintSetupState()
object that is later passed to the register callback functions.
Subclasses can override this to return a subclass of the setup state.
open_resource(resource, mode='rb')
Opens a resource from the application’s resource folder. To see how this works, consider the following folder structure:
/myapplication.py
/schema.sql
/static
/style.css
/templates
/layout.html
/index.html
If you want to open the schema.sql file you would do the
following:
with app.open_resource('schema.sql') as f:
contents = f.read()
do_something_with(contents)
- resource – the name of the resource. To access resources within subfolders use forward slashes as separator.
- mode – resource file opening mode, default is ‘rb’.
record(func)
Registers a function that is called when the blueprint is
registered on the application. This function is called with the
state as argument as returned by the make_setup_state()
method.
record_once(func)
Works like record() but wraps the function in another
function that will ensure the function is only called once. If the
blueprint is registered a second time on the application, the
function passed is not called.
register(app, options, first_registration=False)
Called by Flask.register_blueprint() to register all views
and callbacks registered on the blueprint with the application. Creates
a BlueprintSetupState and calls each record() callback
with it.
- app – The application this blueprint is being registered with.
- options – Keyword arguments forwarded from
register_blueprint(). - first_registration – Whether this is the first time this blueprint has been registered on the application.
register_error_handler(code_or_exception, f)
Non-decorator version of the errorhandler() error attach
function, akin to the register_error_handler()
application-wide function of the Flask object but
for error handlers limited to this blueprint.
New in version 0.11.
root_path = None
Absolute path to the package on the filesystem. Used to look up resources contained in the package.
route(rule, **options)
Like Flask.route() but for a blueprint. The endpoint for the
url_for() function is prefixed with the name of the blueprint.
send_static_file(filename)
Function used internally to send static files from the static folder to the browser.
New in version 0.5.
static_folder
The absolute path to the configured static folder.
static_url_path
The URL prefix that the static route will be registered for.
teardown_app_request(f)
Like Flask.teardown_request() but for a blueprint. Such a
function is executed when tearing down each request, even if outside of
the blueprint.
teardown_request(f)
Like Flask.teardown_request() but for a blueprint. This
function is only executed when tearing down requests handled by a
function of that blueprint. Teardown request functions are executed
when the request context is popped, even when no actual request was
performed.
template_folder = None
Location of the template files to be added to the template lookup.
None if templates should not be added.
url_defaults(f)
Callback function for URL defaults for this blueprint. It’s called with the endpoint and values and should update the values passed in place.
url_value_preprocessor(f)
Registers a function as URL value preprocessor for this blueprint. It’s called before the view functions are called and can modify the url values provided.
Incoming Request Data
class flask.Request(environ, populate_request=True, shallow=False)
The request object used by default in Flask. Remembers the matched endpoint and view arguments.
It is what ends up as request. If you want to replace
the request object used you can subclass this and set
request_class to your subclass.
The request object is a Request subclass and
provides all of the attributes Werkzeug defines plus a few Flask
specific ones.
environ
The underlying WSGI environment.
path
full_path
script_root
url
base_url
url_root
Provides different ways to look at the current IRI. Imagine your application is listening on the following application root:
http://www.example.com/myapplication
And a user requests the following URI:
http://www.example.com/myapplication/%CF%80/page.html?x=y
In this case the values of the above mentioned attributes would be the following:
| [UNKNOWN NODE title_reference] | u'/π/page.html' |
| [UNKNOWN NODE title_reference] | u'/π/page.html?x=y' |
| [UNKNOWN NODE title_reference] | u'/myapplication' |
| [UNKNOWN NODE title_reference] | u'http://www.example.com/myapplication/π/page.html' |
| [UNKNOWN NODE title_reference] | u'http://www.example.com/myapplication/π/page.html?x=y' |
| [UNKNOWN NODE title_reference] | u'http://www.example.com/myapplication/' |
accept_charsets
List of charsets this client supports as
CharsetAccept object.
accept_encodings
List of encodings this client accepts. Encodings in a HTTP term
are compression encodings such as gzip. For charsets have a look at
accept_charset.
accept_languages
List of languages this client accepts as
LanguageAccept object.
accept_mimetypes
List of mimetypes this client supports as
MIMEAccept object.
access_route
If a forwarded header exists this is a list of all ip addresses from the client ip to the last proxy server.
classmethod application(f)
Decorate a function as responder that accepts the request as first
argument. This works like the responder() decorator but the
function is passed the request object as first argument and the
request object will be closed automatically:
@Request.application
def my_wsgi_app(request):
return Response('Hello World!')
As of Werkzeug 0.14 HTTP exceptions are automatically caught and converted to responses instead of failing.
args
The parsed URL parameters (the part in the URL after the question mark).
By default an
ImmutableMultiDict
is returned from this function. This can be changed by setting
parameter_storage_class to a different type. This might
be necessary if the order of the form data is important.
authorization
The [UNKNOWN NODE title_reference] object in parsed form.
base_url
Like url but without the querystring
See also: trusted_hosts.
blueprint
The name of the current blueprint
cache_control
A RequestCacheControl object
for the incoming cache control headers.
close()
Closes associated resources of this request object. This closes all file handles explicitly. You can also use the request object in a with statement which will automatically close it.
New in version 0.9.
content_encoding
The Content-Encoding entity-header field is used as a modifier to the media-type. When present, its value indicates what additional content codings have been applied to the entity-body, and thus what decoding mechanisms must be applied in order to obtain the media-type referenced by the Content-Type header field.
New in version 0.9.
content_length
The Content-Length entity-header field indicates the size of the entity-body in bytes or, in the case of the HEAD method, the size of the entity-body that would have been sent had the request been a GET.
content_md5
The Content-MD5 entity-header field, as defined in RFC 1864, is an MD5 digest of the entity-body for the purpose of providing an end-to-end message integrity check (MIC) of the entity-body. (Note: a MIC is good for detecting accidental modification of the entity-body in transit, but is not proof against malicious attacks.)
New in version 0.9.
content_type
The Content-Type entity-header field indicates the media type of the entity-body sent to the recipient or, in the case of the HEAD method, the media type that would have been sent had the request been a GET.
cookies
A dict with the contents of all cookies transmitted with
the request.
data
Contains the incoming request data as string in case it came with a mimetype Werkzeug does not handle.
date
The Date general-header field represents the date and time at which the message was originated, having the same semantics as orig-date in RFC 822.
dict_storage_class
alias of werkzeug.datastructures.ImmutableTypeConversionDict
endpoint
The endpoint that matched the request. This in combination with
view_args can be used to reconstruct the same or a
modified URL. If an exception happened when matching, this will
be None.
files
MultiDict object containing
all uploaded files. Each key in files is the name from the
<input type="file" name="">. Each value in files is a
Werkzeug FileStorage object.
It basically behaves like a standard file object you know from Python,
with the difference that it also has a
save() function that can
store the file on the filesystem.
Note that files will only contain data if the request method was
POST, PUT or PATCH and the <form> that posted to the request had
enctype="multipart/form-data". It will be empty otherwise.
See the MultiDict /
FileStorage documentation for
more details about the used data structure.
form
The form parameters. By default an
ImmutableMultiDict
is returned from this function. This can be changed by setting
parameter_storage_class to a different type. This might
be necessary if the order of the form data is important.
Please keep in mind that file uploads will not end up here, but instead
in the files attribute.
Changed in version 0.9: Previous to Werkzeug 0.9 this would only contain form data for POST and PUT requests.
form_data_parser_class
alias of werkzeug.formparser.FormDataParser
classmethod from_values(*args, **kwargs)
Create a new request object based on the values provided. If
environ is given missing values are filled from there. This method is
useful for small scripts when you need to simulate a request from an URL.
Do not use this method for unittesting, there is a full featured client
object (Client) that allows to create multipart requests,
support for cookies etc.
This accepts the same options as the
EnvironBuilder.
Changed in version 0.5: This method now accepts the same arguments as
EnvironBuilder. Because of this the
[UNKNOWN NODE title_reference] parameter is now called [UNKNOWN NODE title_reference].
full_path
Requested path as unicode, including the query string.
get_data(cache=True, as_text=False, parse_form_data=False)
This reads the buffered incoming data from the client into one bytestring. By default this is cached but that behavior can be changed by setting [UNKNOWN NODE title_reference] to [UNKNOWN NODE title_reference].
Usually it’s a bad idea to call this method without checking the content length first as a client could send dozens of megabytes or more to cause memory problems on the server.
Note that if the form data was already parsed this method will not return anything as form data parsing does not cache the data like this method does. To implicitly invoke form data parsing function set [UNKNOWN NODE title_reference] to [UNKNOWN NODE title_reference]. When this is done the return value of this method will be an empty string if the form parser handles the data. This generally is not necessary as if the whole data is cached (which is the default) the form parser will used the cached data to parse the form data. Please be generally aware of checking the content length first in any case before calling this method to avoid exhausting server memory.
If [UNKNOWN NODE title_reference] is set to [UNKNOWN NODE title_reference] the return value will be a decoded unicode string.
New in version 0.9.
get_json(force=False, silent=False, cache=True)
Parse and return the data as JSON. If the mimetype does not indicate
JSON (application/json, see is_json()), this returns
None unless force is true. If parsing fails,
on_json_loading_failed() is called and its return value is used
as the return value.
- force – Ignore the mimetype and always try to parse JSON.
- silent – Silence parsing errors and return
Noneinstead. - cache – Store the parsed JSON to return for subsequent calls.
headers
The headers from the WSGI environ as immutable
EnvironHeaders.
host
Just the host including the port if available.
See also: trusted_hosts.
host_url
Just the host with scheme as IRI.
See also: trusted_hosts.
if_match
An object containing all the etags in the [UNKNOWN NODE title_reference] header.
if_modified_since
The parsed [UNKNOWN NODE title_reference] header as datetime object.
if_none_match
An object containing all the etags in the [UNKNOWN NODE title_reference] header.
if_range
The parsed [UNKNOWN NODE title_reference] header.
New in version 0.7.
if_unmodified_since
The parsed [UNKNOWN NODE title_reference] header as datetime object.
is_json
Check if the mimetype indicates JSON data, either
application/json or application/*+json.
New in version 0.11.
is_multiprocess
boolean that is [UNKNOWN NODE title_reference] if the application is served by a WSGI server that spawns multiple processes.
is_multithread
boolean that is [UNKNOWN NODE title_reference] if the application is served by a multithreaded WSGI server.
is_run_once
boolean that is [UNKNOWN NODE title_reference] if the application will be executed only once in a process lifetime. This is the case for CGI for example, but it’s not guaranteed that the execution only happens one time.
is_secure
[UNKNOWN NODE title_reference] if the request is secure.
is_xhr
True if the request was triggered via a JavaScript XMLHttpRequest.
This only works with libraries that support the X-Requested-With
header and set it to “XMLHttpRequest”. Libraries that do that are
prototype, jQuery and Mochikit and probably some more.
Deprecated since version 0.13: X-Requested-With is not standard and is unreliable.
json
This will contain the parsed JSON data if the mimetype indicates
JSON (application/json, see is_json()), otherwise it
will be None.
list_storage_class
make_form_data_parser()
Creates the form data parser. Instantiates the
form_data_parser_class with some parameters.
New in version 0.8.
max_content_length
Read-only view of the MAX_CONTENT_LENGTH config key.
max_forwards
The Max-Forwards request-header field provides a mechanism with the TRACE and OPTIONS methods to limit the number of proxies or gateways that can forward the request to the next inbound server.
method
The request method. (For example 'GET' or 'POST').
mimetype
Like content_type, but without parameters (eg, without
charset, type etc.) and always lowercase. For example if the content
type is text/HTML; charset=utf-8 the mimetype would be
'text/html'.
mimetype_params
The mimetype parameters as dict. For example if the content
type is text/html; charset=utf-8 the params would be
{'charset': 'utf-8'}.
on_json_loading_failed(e)
Called if get_json() parsing fails and isn’t silenced. If
this method returns a value, it is used as the return value for
get_json(). The default implementation raises a
BadRequest exception.
Changed in version 0.10: Raise a BadRequest error instead of returning an error
message as JSON. If you want that behavior you can add it by
subclassing.
New in version 0.8.
parameter_storage_class
path
Requested path as unicode. This works a bit like the regular path info in the WSGI environment but will always include a leading slash, even if the URL root is accessed.
pragma
The Pragma general-header field is used to include implementation-specific directives that might apply to any recipient along the request/response chain. All pragma directives specify optional behavior from the viewpoint of the protocol; however, some systems MAY require that behavior be consistent with the directives.
query_string
The URL parameters as raw bytestring.
range
The parsed [UNKNOWN NODE title_reference] header.
New in version 0.7.
referrer
The Referer[sic] request-header field allows the client to specify, for the server’s benefit, the address (URI) of the resource from which the Request-URI was obtained (the “referrer”, although the header field is misspelled).
remote_addr
The remote address of the client.
remote_user
If the server supports user authentication, and the script is protected, this attribute contains the username the user has authenticated as.
routing_exception = None
If matching the URL failed, this is the exception that will be
raised / was raised as part of the request handling. This is
usually a NotFound exception or
something similar.
scheme
URL scheme (http or https).
New in version 0.7.
script_root
The root path of the script without the trailing slash.
stream
If the incoming form data was not encoded with a known mimetype
the data is stored unmodified in this stream for consumption. Most
of the time it is a better idea to use data which will give
you that data as a string. The stream only returns the data once.
Unlike input_stream this stream is properly guarded that you
can’t accidentally read past the length of the input. Werkzeug will
internally always refer to this stream to read data which makes it
possible to wrap this object with a stream that does filtering.
Changed in version 0.9: This stream is now always available but might be consumed by the form parser later on. Previously the stream was only set if no parsing happened.
url
The reconstructed current URL as IRI.
See also: trusted_hosts.
url_charset
The charset that is assumed for URLs. Defaults to the value
of charset.
New in version 0.6.
url_root
The full URL root (with hostname), this is the application
root as IRI.
See also: trusted_hosts.
url_rule = None
The internal URL rule that matched the request. This can be
useful to inspect which methods are allowed for the URL from
a before/after handler (request.url_rule.methods) etc.
Though if the request’s method was invalid for the URL rule,
the valid list is available in routing_exception.valid_methods
instead (an attribute of the Werkzeug exception MethodNotAllowed)
because the request was never internally bound.
New in version 0.6.
user_agent
The current user agent.
values
A werkzeug.datastructures.CombinedMultiDict that combines
args and form.
view_args = None
A dict of view arguments that matched the request. If an exception
happened when matching, this will be None.
want_form_data_parsed
Returns True if the request method carries content. As of Werkzeug 0.9 this will be the case if a content type is transmitted.
New in version 0.8.
flask.request
To access incoming request data, you can use the global [UNKNOWN NODE title_reference] object. Flask parses incoming request data for you and gives you access to it through that global object. Internally Flask makes sure that you always get the correct data for the active thread if you are in a multithreaded environment.
This is a proxy. See Notes On Proxies for more information.
The request object is an instance of a Request
subclass and provides all of the attributes Werkzeug defines. This
just shows a quick overview of the most important ones.
Response Objects
class flask.Response(response=None, status=None, headers=None, mimetype=None, content_type=None, direct_passthrough=False)
The response object that is used by default in Flask. Works like the
response object from Werkzeug but is set to have an HTML mimetype by
default. Quite often you don’t have to create this object yourself because
make_response() will take care of that for you.
If you want to replace the response object used you can subclass this and
set response_class to your subclass.
Changed in version 1.0: JSON support is added to the response, like the request. This is useful when testing to get the test client response data as JSON.
headers
A Headers object representing the response headers.
status
A string with a response status.
status_code
The response status as integer.
data
A descriptor that calls get_data() and set_data(). This
should not be used and will eventually get deprecated.
get_json(force=False, silent=False, cache=True)
Parse and return the data as JSON. If the mimetype does not indicate
JSON (application/json, see is_json()), this returns
None unless force is true. If parsing fails,
on_json_loading_failed() is called and its return value is used
as the return value.
- force – Ignore the mimetype and always try to parse JSON.
- silent – Silence parsing errors and return
Noneinstead. - cache – Store the parsed JSON to return for subsequent calls.
is_json
Check if the mimetype indicates JSON data, either
application/json or application/*+json.
New in version 0.11.
mimetype
The mimetype (content type without charset etc.)
set_cookie(key, value='', max_age=None, expires=None, path='/', domain=None, secure=False, httponly=False, samesite=None)
Sets a cookie. The parameters are the same as in the cookie [UNKNOWN NODE title_reference] object in the Python standard library but it accepts unicode data, too.
A warning is raised if the size of the cookie header exceeds
max_cookie_size, but the header will still be set.
- key – the key (name) of the cookie to be set.
- value – the value of the cookie.
- max_age – should be a number of seconds, or [UNKNOWN NODE title_reference] (default) if the cookie should last only as long as the client’s browser session.
- expires – should be a [UNKNOWN NODE title_reference] object or UNIX timestamp.
- path – limits the cookie to a given path, per default it will span the whole domain.
- domain – if you want to set a cross-domain cookie. For example,
domain=".example.com"will set a cookie that is readable by the domainwww.example.com,foo.example.cometc. Otherwise, a cookie will only be readable by the domain that set it. - secure – If [UNKNOWN NODE title_reference], the cookie will only be available via HTTPS
- httponly – disallow JavaScript to access the cookie. This is an extension to the cookie standard and probably not supported by all browsers.
- samesite – Limits the scope of the cookie such that it will only be attached to requests if those requests are “same-site”.
Sessions
If you have set Flask.secret_key (or configured it from
SECRET_KEY) you can use sessions in Flask applications. A session makes
it possible to remember information from one request to another. The way Flask
does this is by using a signed cookie. The user can look at the session
contents, but can’t modify it unless they know the secret key, so make sure to
set that to something complex and unguessable.
To access the current session you can use the session object:
class flask.session
The session object works pretty much like an ordinary dict, with the difference that it keeps track on modifications.
This is a proxy. See Notes On Proxies for more information.
The following attributes are interesting:
new
True if the session is new, False otherwise.
modified
True if the session object detected a modification. Be advised
that modifications on mutable structures are not picked up
automatically, in that situation you have to explicitly set the
attribute to True yourself. Here an example:
# this change is not picked up because a mutable object (here
# a list) is changed.
session['objects'].append(42)
# so mark it as modified yourself
session.modified = True
permanent
If set to True the session lives for
permanent_session_lifetime seconds. The
default is 31 days. If set to False (which is the default) the
session will be deleted when the user closes the browser.
Session Interface
New in version 0.8.
The session interface provides a simple way to replace the session implementation that Flask is using.
class flask.sessions.SessionInterface
The basic interface you have to implement in order to replace the
default session interface which uses werkzeug’s securecookie
implementation. The only methods you have to implement are
open_session() and save_session(), the others have
useful defaults which you don’t need to change.
The session object returned by the open_session() method has to
provide a dictionary like interface plus the properties and methods
from the SessionMixin. We recommend just subclassing a dict
and adding that mixin:
class Session(dict, SessionMixin):
pass
If open_session() returns None Flask will call into
make_null_session() to create a session that acts as replacement
if the session support cannot work because some requirement is not
fulfilled. The default NullSession class that is created
will complain that the secret key was not set.
To replace the session interface on an application all you have to do
is to assign flask.Flask.session_interface:
app = Flask(__name__)
app.session_interface = MySessionInterface()
New in version 0.8.
get_cookie_domain(app)
Returns the domain that should be set for the session cookie.
Uses SESSION_COOKIE_DOMAIN if it is configured, otherwise
falls back to detecting the domain based on SERVER_NAME.
Once detected (or if not set at all), SESSION_COOKIE_DOMAIN is
updated to avoid re-running the logic.
get_cookie_httponly(app)
Returns True if the session cookie should be httponly. This
currently just returns the value of the SESSION_COOKIE_HTTPONLY
config var.
get_cookie_path(app)
Returns the path for which the cookie should be valid. The
default implementation uses the value from the SESSION_COOKIE_PATH
config var if it’s set, and falls back to APPLICATION_ROOT or
uses / if it’s None.
get_cookie_samesite(app)
Return 'Strict' or 'Lax' if the cookie should use the
SameSite attribute. This currently just returns the value of
the SESSION_COOKIE_SAMESITE setting.
get_cookie_secure(app)
Returns True if the cookie should be secure. This currently
just returns the value of the SESSION_COOKIE_SECURE setting.
get_expiration_time(app, session)
A helper method that returns an expiration date for the session
or None if the session is linked to the browser session. The
default implementation returns now + the permanent session
lifetime configured on the application.
is_null_session(obj)
Checks if a given object is a null session. Null sessions are not asked to be saved.
This checks if the object is an instance of null_session_class
by default.
make_null_session(app)
Creates a null session which acts as a replacement object if the real session support could not be loaded due to a configuration error. This mainly aids the user experience because the job of the null session is to still support lookup without complaining but modifications are answered with a helpful error message of what failed.
This creates an instance of null_session_class by default.
null_session_class
make_null_session() will look here for the class that should
be created when a null session is requested. Likewise the
is_null_session() method will perform a typecheck against
this type.
alias of NullSession
open_session(app, request)
This method has to be implemented and must either return None
in case the loading failed because of a configuration error or an
instance of a session object which implements a dictionary like
interface + the methods and attributes on SessionMixin.
pickle_based = False
A flag that indicates if the session interface is pickle based. This can be used by Flask extensions to make a decision in regards to how to deal with the session object.
New in version 0.10.
save_session(app, session, response)
This is called for actual sessions returned by open_session()
at the end of the request. This is still called during a request
context so if you absolutely need access to the request you can do
that.
should_set_cookie(app, session)
Used by session backends to determine if a Set-Cookie header
should be set for this session cookie for this response. If the session
has been modified, the cookie is set. If the session is permanent and
the SESSION_REFRESH_EACH_REQUEST config is true, the cookie is
always set.
This check is usually skipped if the session was deleted.
New in version 0.11.
class flask.sessions.SecureCookieSessionInterface
The default session interface that stores sessions in signed cookies
through the itsdangerous module.
static digest_method()
the hash function to use for the signature. The default is sha1
key_derivation = 'hmac'
the name of the itsdangerous supported key derivation. The default is hmac.
open_session(app, request)
This method has to be implemented and must either return None
in case the loading failed because of a configuration error or an
instance of a session object which implements a dictionary like
interface + the methods and attributes on SessionMixin.
salt = 'cookie-session'
the salt that should be applied on top of the secret key for the signing of cookie based sessions.
save_session(app, session, response)
This is called for actual sessions returned by open_session()
at the end of the request. This is still called during a request
context so if you absolutely need access to the request you can do
that.
serializer = <flask.json.tag.TaggedJSONSerializer object>
A python serializer for the payload. The default is a compact JSON derived serializer with support for some extra Python types such as datetime objects or tuples.
session_class
alias of SecureCookieSession
class flask.sessions.SecureCookieSession(initial=None)
Base class for sessions based on signed cookies.
This session backend will set the modified and
accessed attributes. It cannot reliably track whether a
session is new (vs. empty), so new remains hard coded to
False.
accessed = False
header, which allows caching proxies to cache different pages for different users.
get(k[, d]) → D[k] if k in D, else d. d defaults to None.
modified = False
When data is changed, this is set to True. Only the session
dictionary itself is tracked; if the session contains mutable
data (for example a nested dict) then this must be set to
True manually when modifying that data. The session cookie
will only be written to the response if this is True.
setdefault(k[, d]) → D.get(k,d), also set D[k]=d if k not in D
class flask.sessions.NullSession(initial=None)
Class used to generate nicer error messages if sessions are not available. Will still allow read-only access to the empty session but fail on setting.
class flask.sessions.SessionMixin
Expands a basic dictionary with session attributes.
accessed = True
Some implementations can detect when session data is read or
written and set this when that happens. The mixin default is hard
coded to True.
modified = True
Some implementations can detect changes to the session and set
this when that happens. The mixin default is hard coded to
True.
permanent
This reflects the '_permanent' key in the dict.
Notice
The PERMANENT_SESSION_LIFETIME config key can also be an integer
starting with Flask 0.8. Either catch this down yourself or use
the permanent_session_lifetime attribute on the
app which converts the result to an integer automatically.
Test Client
class flask.testing.FlaskClient(*args, **kwargs)
Works like a regular Werkzeug test client but has some knowledge about
how Flask works to defer the cleanup of the request context stack to the
end of a with body when used in a with statement. For general
information about how to use this class refer to
werkzeug.test.Client.
Changed in version 0.12: [UNKNOWN NODE title_reference] includes preset default environment, which can be set after instantiation of the [UNKNOWN NODE title_reference] object in [UNKNOWN NODE title_reference].
Basic usage is outlined in the Testing Flask Applications chapter.
open(*args, **kwargs)
Takes the same arguments as the EnvironBuilder class with
some additions: You can provide a EnvironBuilder or a WSGI
environment as only argument instead of the EnvironBuilder
arguments and two optional keyword arguments ([UNKNOWN NODE title_reference], [UNKNOWN NODE title_reference])
that change the type of the return value or the way the application is
executed.
Changed in version 0.5: If a dict is provided as file in the dict for the [UNKNOWN NODE title_reference] parameter
the content type has to be called [UNKNOWN NODE title_reference] now instead of
[UNKNOWN NODE title_reference]. This change was made for consistency with
werkzeug.FileWrapper.
The [UNKNOWN NODE title_reference] parameter was added to open().Additional parameters:
- as_tuple – Returns a tuple in the form
(environ, result) - buffered – Set this to True to buffer the application run. This will automatically close the application for you as well.
- follow_redirects – Set this to True if the [UNKNOWN NODE title_reference] should follow HTTP redirects.
session_transaction(*args, **kwargs)
When used in combination with a with statement this opens a
session transaction. This can be used to modify the session that
the test client uses. Once the with block is left the session is
stored back.
with client.session_transaction() as session:
session['value'] = 42
Internally this is implemented by going through a temporary test
request context and since session handling could depend on
request variables this function accepts the same arguments as
test_request_context() which are directly
passed through.
Test CLI Runner
class flask.testing.FlaskCliRunner(app, **kwargs)
A CliRunner for testing a Flask app’s
CLI commands. Typically created using
test_cli_runner(). See Testing CLI Commands.
invoke(cli=None, args=None, **kwargs)
Invokes a CLI command in an isolated environment. See
CliRunner.invoke for
full method documentation. See Testing CLI Commands for examples.
If the obj argument is not given, passes an instance of
ScriptInfo that knows how to load the Flask
app being tested.
- cli – Command object to invoke. Default is the app’s
cligroup. - args – List of strings to invoke the command with.
Result object.Application Globals
To share data that is valid for one request only from one function to
another, a global variable is not good enough because it would break in
threaded environments. Flask provides you with a special object that
ensures it is only valid for the active request and that will return
different values for each request. In a nutshell: it does the right
thing, like it does for request and session.
flask.g
Just store on this whatever you want. For example a database connection or the user that is currently logged in.
Starting with Flask 0.10 this is stored on the application context and no longer on the request context which means it becomes available if only the application context is bound and not yet a request. This is especially useful when combined with the Faking Resources and Context pattern for testing.
Additionally as of 0.10 you can use the get() method to
get an attribute or None (or the second argument) if it’s not set.
These two usages are now equivalent:
user = getattr(flask.g, 'user', None)
user = flask.g.get('user', None)
It’s now also possible to use the in operator on it to see if an
attribute is defined and it yields all keys on iteration.
As of 0.11 you can use pop() and setdefault() in the same
way you would use them on a dictionary.
This is a proxy. See Notes On Proxies for more information.
Useful Functions and Classes
flask.current_app
Points to the application handling the request. This is useful for
extensions that want to support multiple applications running side
by side. This is powered by the application context and not by the
request context, so you can change the value of this proxy by
using the app_context() method.
This is a proxy. See Notes On Proxies for more information.
flask.has_request_context()
If you have code that wants to test if a request context is there or not this function can be used. For instance, you may want to take advantage of request information if the request object is available, but fail silently if it is unavailable.
class User(db.Model):
def __init__(self, username, remote_addr=None):
self.username = username
if remote_addr is None and has_request_context():
remote_addr = request.remote_addr
self.remote_addr = remote_addr
Alternatively you can also just test any of the context bound objects
(such as request or g for truthness):
class User(db.Model):
def __init__(self, username, remote_addr=None):
self.username = username
if remote_addr is None and request:
remote_addr = request.remote_addr
self.remote_addr = remote_addr
New in version 0.7.
flask.copy_current_request_context(f)
A helper function that decorates a function to retain the current request context. This is useful when working with greenlets. The moment the function is decorated a copy of the request context is created and then pushed when the function is called.
Example:
import gevent
from flask import copy_current_request_context
@app.route('/')
def index():
@copy_current_request_context
def do_some_work():
# do some work here, it can access flask.request like you
# would otherwise in the view function.
...
gevent.spawn(do_some_work)
return 'Regular response'
New in version 0.10.
flask.has_app_context()
Works like has_request_context() but for the application
context. You can also just do a boolean check on the
current_app object instead.
New in version 0.9.
flask.url_for(endpoint, **values)
Generates a URL to the given endpoint with the method provided.
Variable arguments that are unknown to the target endpoint are appended
to the generated URL as query arguments. If the value of a query argument
is None, the whole pair is skipped. In case blueprints are active
you can shortcut references to the same blueprint by prefixing the
local endpoint with a dot (.).
This will reference the index function local to the current blueprint:
url_for('.index')
For more information, head over to the Quickstart.
To integrate applications, Flask has a hook to intercept URL build
errors through Flask.url_build_error_handlers. The [UNKNOWN NODE title_reference]
function results in a BuildError when the current
app does not have a URL for the given endpoint and values. When it does, the
current_app calls its url_build_error_handlers if
it is not None, which can return a string to use as the result of
[UNKNOWN NODE title_reference] (instead of [UNKNOWN NODE title_reference]’s default to raise the
BuildError exception) or re-raise the exception.
An example:
def external_url_handler(error, endpoint, values):
"Looks up an external URL when `url_for` cannot build a URL."
# This is an example of hooking the build_error_handler.
# Here, lookup_url is some utility function you've built
# which looks up the endpoint in some external URL registry.
url = lookup_url(endpoint, **values)
if url is None:
# External lookup did not have a URL.
# Re-raise the BuildError, in context of original traceback.
exc_type, exc_value, tb = sys.exc_info()
if exc_value is error:
raise exc_type, exc_value, tb
else:
raise error
# url_for will use this result, instead of raising BuildError.
return url
app.url_build_error_handlers.append(external_url_handler)
Here, [UNKNOWN NODE title_reference] is the instance of BuildError, and
[UNKNOWN NODE title_reference] and [UNKNOWN NODE title_reference] are the arguments passed into [UNKNOWN NODE title_reference]. Note
that this is for building URLs outside the current application, and not for
handling 404 NotFound errors.
New in version 0.10: The [UNKNOWN NODE title_reference] parameter was added.
New in version 0.9: The [UNKNOWN NODE title_reference] and [UNKNOWN NODE title_reference] parameters were added.
New in version 0.9: Calls Flask.handle_build_error() on
BuildError.
- endpoint – the endpoint of the URL (name of the function)
- values – the variable arguments of the URL rule
- _external – if set to
True, an absolute URL is generated. Server address can be changed viaSERVER_NAMEconfiguration variable which defaults to [UNKNOWN NODE title_reference]. - _scheme – a string specifying the desired URL scheme. The [UNKNOWN NODE title_reference]
parameter must be set to
Trueor aValueErroris raised. The default behavior uses the same scheme as the current request, orPREFERRED_URL_SCHEMEfrom the app configuration if no request context is available. As of Werkzeug 0.10, this also can be set to an empty string to build protocol-relative URLs. - _anchor – if provided this is added as anchor to the URL.
- _method – if provided this explicitly specifies an HTTP method.
flask.abort(status, *args, **kwargs)
Raises an HTTPException for the given status code or WSGI
application:
abort(404) # 404 Not Found
abort(Response('Hello World'))
Can be passed a WSGI application or a status code. If a status code is given it’s looked up in the list of exceptions and will raise that exception, if passed a WSGI application it will wrap it in a proxy WSGI exception and raise that:
abort(404)
abort(Response('Hello World'))
flask.redirect(location, code=302, Response=None)
Returns a response object (a WSGI application) that, if called, redirects the client to the target location. Supported codes are 301, 302, 303, 305, and 307. 300 is not supported because it’s not a real redirect and 304 because it’s the answer for a request with a request with defined If-Modified-Since headers.
New in version 0.6: The location can now be a unicode string that is encoded using
the iri_to_uri() function.
New in version 0.10: The class used for the Response object can now be passed in.
- location – the location the response should redirect to.
- code – the redirect status code. defaults to 302.
- Response (
class) – a Response class to use when instantiating a response. The default iswerkzeug.wrappers.Responseif unspecified.
flask.make_response(*args)
Sometimes it is necessary to set additional headers in a view. Because views do not have to return response objects but can return a value that is converted into a response object by Flask itself, it becomes tricky to add headers to it. This function can be called instead of using a return and you will get a response object which you can use to attach headers.
If view looked like this and you want to add a new header:
def index():
return render_template('index.html', foo=42)
You can now do something like this:
def index():
response = make_response(render_template('index.html', foo=42))
response.headers['X-Parachutes'] = 'parachutes are cool'
return response
This function accepts the very same arguments you can return from a view function. This for example creates a response with a 404 error code:
response = make_response(render_template('not_found.html'), 404)
The other use case of this function is to force the return value of a view function into a response which is helpful with view decorators:
response = make_response(view_function())
response.headers['X-Parachutes'] = 'parachutes are cool'
Internally this function does the following things:
- if no arguments are passed, it creates a new response argument
- if one argument is passed,
flask.Flask.make_response()is invoked with it. - if more than one argument is passed, the arguments are passed
to the
flask.Flask.make_response()function as tuple.
New in version 0.6.
flask.after_this_request(f)
Executes a function after this request. This is useful to modify response objects. The function is passed the response object and has to return the same or a new one.
Example:
@app.route('/')
def index():
@after_this_request
def add_header(response):
response.headers['X-Foo'] = 'Parachute'
return response
return 'Hello World!'
This is more useful if a function other than the view function wants to modify a response. For instance think of a decorator that wants to add some headers without converting the return value into a response object.
New in version 0.9.
flask.send_file(filename_or_fp, mimetype=None, as_attachment=False, attachment_filename=None, add_etags=True, cache_timeout=None, conditional=False, last_modified=None)
Sends the contents of a file to the client. This will use the
most efficient method available and configured. By default it will
try to use the WSGI server’s file_wrapper support. Alternatively
you can set the application’s use_x_sendfile attribute
to True to directly emit an X-Sendfile header. This however
requires support of the underlying webserver for X-Sendfile.
By default it will try to guess the mimetype for you, but you can also explicitly provide one. For extra security you probably want to send certain files as attachment (HTML for instance). The mimetype guessing requires a [UNKNOWN NODE title_reference] or an [UNKNOWN NODE title_reference] to be provided.
ETags will also be attached automatically if a [UNKNOWN NODE title_reference] is provided. You can turn this off by setting [UNKNOWN NODE title_reference].
If [UNKNOWN NODE title_reference] and [UNKNOWN NODE title_reference] is provided, this method will try to upgrade the response stream to support range requests. This will allow the request to be answered with partial content response.
Please never pass filenames to this function from user sources;
you should use send_from_directory() instead.
New in version 0.2.
New in version 0.5: The [UNKNOWN NODE title_reference], [UNKNOWN NODE title_reference] and [UNKNOWN NODE title_reference] parameters were added. The default behavior is now to attach etags.
Changed in version 0.7: mimetype guessing and etag support for file objects was deprecated because it was unreliable. Pass a filename if you are able to, otherwise attach an etag yourself. This functionality will be removed in Flask 1.0
Changed in version 0.9: cache_timeout pulls its default from application config, when None.
Changed in version 0.12: The filename is no longer automatically inferred from file objects. If you want to use automatic mimetype and etag support, pass a filepath via [UNKNOWN NODE title_reference] or [UNKNOWN NODE title_reference].
Changed in version 0.12: The [UNKNOWN NODE title_reference] is preferred over [UNKNOWN NODE title_reference] for MIME-type detection.
Changed in version 0.13: UTF-8 filenames, as specified in RFC 2231, are supported.
- filename_or_fp – the filename of the file to send.
This is relative to the
root_pathif a relative path is specified. Alternatively a file object might be provided in which caseX-Sendfilemight not work and fall back to the traditional method. Make sure that the file pointer is positioned at the start of data to send before callingsend_file(). - mimetype – the mimetype of the file if provided. If a file path is given, auto detection happens as fallback, otherwise an error will be raised.
- as_attachment – set to
Trueif you want to send this file with aContent-Disposition: attachmentheader. - attachment_filename – the filename for the attachment if it differs from the file’s filename.
- add_etags – set to
Falseto disable attaching of etags. - conditional – set to
Trueto enable conditional responses. - cache_timeout – the timeout in seconds for the headers. When
None(default), this value is set byget_send_file_max_age()ofcurrent_app. - last_modified – set the
Last-Modifiedheader to this value, adatetimeor timestamp. If a file was passed, this overrides its mtime.
flask.send_from_directory(directory, filename, **options)
Send a file from a given directory with send_file(). This
is a secure way to quickly expose static files from an upload folder
or something similar.
Example usage:
@app.route('/uploads/<path:filename>')
def download_file(filename):
return send_from_directory(app.config['UPLOAD_FOLDER'],
filename, as_attachment=True)
Sending files and Performance
It is strongly recommended to activate either X-Sendfile support in
your webserver or (if no authentication happens) to tell the webserver
to serve files for the given path on its own without calling into the
web application for improved performance.
New in version 0.5.
- directory – the directory where all the files are stored.
- filename – the filename relative to that directory to download.
- options – optional keyword arguments that are directly
forwarded to
send_file().
flask.safe_join(directory, *pathnames)
Safely join [UNKNOWN NODE title_reference] and zero or more untrusted [UNKNOWN NODE title_reference] components.
Example usage:
@app.route('/wiki/<path:filename>')
def wiki_page(filename):
filename = safe_join(app.config['WIKI_FOLDER'], filename)
with open(filename, 'rb') as fd:
content = fd.read() # Read and process the file content...
- directory – the trusted base directory.
- pathnames – the untrusted pathnames relative to that directory.
NotFound if one or more passed
paths fall out of its boundaries.flask.escape(s) → markup
Convert the characters &, <, >, ‘, and ” in string s to HTML-safe sequences. Use this if you need to display text that might contain such characters in HTML. Marks return value as markup string.
class flask.Markup
Marks a string as being safe for inclusion in HTML/XML output without
needing to be escaped. This implements the [UNKNOWN NODE title_reference] interface a couple
of frameworks and web applications use. Markup is a direct
subclass of [UNKNOWN NODE title_reference] and provides all the methods of [UNKNOWN NODE title_reference] just that
it escapes arguments passed and always returns [UNKNOWN NODE title_reference].
The [UNKNOWN NODE title_reference] function returns markup objects so that double escaping can’t happen.
The constructor of the Markup class can be used for three
different things: When passed an unicode object it’s assumed to be safe,
when passed an object with an HTML representation (has an [UNKNOWN NODE title_reference]
method) that representation is used, otherwise the object passed is
converted into a unicode string and then assumed to be safe:
If you want object passed being always treated as unsafe you can use the
escape() classmethod to create a Markup object:
Operations on a markup string are markup aware which means that all
arguments are passed through the escape() function:
classmethod escape(s)
Escape the string. Works like escape() with the difference
that for subclasses of Markup this function would return the
correct subclass.
striptags()
Unescape markup into an text_type string and strip all tags. This also resolves known HTML4 and XHTML entities. Whitespace is normalized to one:
[UNKNOWN NODE doctest_block]unescape()
Unescape markup again into an text_type string. This also resolves known HTML4 and XHTML entities:
[UNKNOWN NODE doctest_block]Message Flashing
flask.flash(message, category='message')
Flashes a message to the next request. In order to remove the
flashed message from the session and to display it to the user,
the template has to call get_flashed_messages().
Changed in version 0.3: [UNKNOWN NODE title_reference] parameter added.
- message – the message to be flashed.
- category – the category for the message. The following values
are recommended:
'message'for any kind of message,'error'for errors,'info'for information messages and'warning'for warnings. However any kind of string can be used as category.
flask.get_flashed_messages(with_categories=False, category_filter=[])
Pulls all flashed messages from the session and returns them.
Further calls in the same request to the function will return
the same messages. By default just the messages are returned,
but when [UNKNOWN NODE title_reference] is set to True, the return value will
be a list of tuples in the form (category, message) instead.
Filter the flashed messages to one or more categories by providing those categories in [UNKNOWN NODE title_reference]. This allows rendering categories in separate html blocks. The [UNKNOWN NODE title_reference] and [UNKNOWN NODE title_reference] arguments are distinct:
- [UNKNOWN NODE title_reference] controls whether categories are returned with message
text (
Truegives a tuple, whereFalsegives just the message text). - [UNKNOWN NODE title_reference] filters the messages down to only those matching the provided categories.
See Message Flashing for examples.
Changed in version 0.3: [UNKNOWN NODE title_reference] parameter added.
Changed in version 0.9: [UNKNOWN NODE title_reference] parameter added.
- with_categories – set to
Trueto also receive categories. - category_filter – whitelist of categories to limit return values
JSON Support
Flask uses simplejson for the JSON implementation. Since simplejson
is provided by both the standard library as well as extension, Flask will
try simplejson first and then fall back to the stdlib json module. On top
of that it will delegate access to the current application’s JSON encoders
and decoders for easier customization.
So for starters instead of doing:
try:
import simplejson as json
except ImportError:
import json
You can instead just do this:
from flask import json
For usage examples, read the json documentation in the standard
library. The following extensions are by default applied to the stdlib’s
JSON module:
datetimeobjects are serialized as RFC 822 strings.- Any object with an
__html__method (likeMarkup) will have that method called and then the return value is serialized as string.
The htmlsafe_dumps() function of this json module is also available
as filter called |tojson in Jinja2. Note that inside script
tags no escaping must take place, so make sure to disable escaping
with |safe if you intend to use it inside script tags unless
you are using Flask 0.10 which implies that:
<script type=text/javascript>
doSomethingWith({{ user.username|tojson|safe }});
</script>
Auto-Sort JSON Keys
The configuration variable JSON_SORT_KEYS (Configuration Handling) can be
set to false to stop Flask from auto-sorting keys. By default sorting
is enabled and outside of the app context sorting is turned on.
Notice that disabling key sorting can cause issues when using content based HTTP caches and Python’s hash randomization feature.
flask.json.jsonify(*args, **kwargs)
This function wraps dumps() to add a few enhancements that make
life easier. It turns the JSON output into a Response
object with the application/json mimetype. For convenience, it
also converts multiple arguments into an array or multiple keyword arguments
into a dict. This means that both jsonify(1,2,3) and
jsonify([1,2,3]) serialize to [1,2,3].
For clarity, the JSON serialization behavior has the following differences
from dumps():
- Single argument: Passed straight through to
dumps(). - Multiple arguments: Converted to an array before being passed to
dumps(). - Multiple keyword arguments: Converted to a dict before being passed to
dumps(). - Both args and kwargs: Behavior undefined and will throw an exception.
Example usage:
from flask import jsonify
@app.route('/_get_current_user')
def get_current_user():
return jsonify(username=g.user.username,
email=g.user.email,
id=g.user.id)
This will send a JSON response like this to the browser:
{
"username": "admin",
"email": "admin@localhost",
"id": 42
}
Changed in version 0.11: Added support for serializing top-level arrays. This introduces a security risk in ancient browsers. See JSON Security for details.
This function’s response will be pretty printed if the
JSONIFY_PRETTYPRINT_REGULAR config parameter is set to True or the
Flask app is running in debug mode. Compressed (not pretty) formatting
currently means no indents and no spaces after separators.
New in version 0.2.
flask.json.dumps(obj, **kwargs)
Serialize obj to a JSON formatted str by using the application’s
configured encoder (json_encoder) if there is an
application on the stack.
This function can return unicode strings or ascii-only bytestrings by
default which coerce into unicode strings automatically. That behavior by
default is controlled by the JSON_AS_ASCII configuration variable
and can be overridden by the simplejson ensure_ascii parameter.
flask.json.dump(obj, fp, **kwargs)
Like dumps() but writes into a file object.
flask.json.loads(s, **kwargs)
Unserialize a JSON object from a string s by using the application’s
configured decoder (json_decoder) if there is an
application on the stack.
flask.json.load(fp, **kwargs)
Like loads() but reads from a file object.
class flask.json.JSONEncoder(skipkeys=False, ensure_ascii=True, check_circular=True, allow_nan=True, sort_keys=False, indent=None, separators=None, encoding='utf-8', default=None)
The default Flask JSON encoder. This one extends the default simplejson
encoder by also supporting datetime objects, UUID as well as
Markup objects which are serialized as RFC 822 datetime strings (same
as the HTTP date format). In order to support more data types override the
default() method.
default(o)
Implement this method in a subclass such that it returns a
serializable object for o, or calls the base implementation (to
raise a TypeError).
For example, to support arbitrary iterators, you could implement default like this:
def default(self, o):
try:
iterable = iter(o)
except TypeError:
pass
else:
return list(iterable)
return JSONEncoder.default(self, o)
class flask.json.JSONDecoder(encoding=None, object_hook=None, parse_float=None, parse_int=None, parse_constant=None, strict=True, object_pairs_hook=None)
The default JSON decoder. This one does not change the behavior from
the default simplejson decoder. Consult the json documentation
for more information. This decoder is not only used for the load
functions of this module but also Request.
Tagged JSON
A compact representation for lossless serialization of non-standard JSON types.
SecureCookieSessionInterface uses this to serialize
the session data, but it may be useful in other places. It can be extended to
support other types.
class flask.json.tag.TaggedJSONSerializer
Serializer that uses a tag system to compactly represent objects that
are not JSON types. Passed as the intermediate serializer to
itsdangerous.Serializer.
The following extra types are supported:
default_tags = [<class 'flask.json.tag.TagDict'>, <class 'flask.json.tag.PassDict'>, <class 'flask.json.tag.TagTuple'>, <class 'flask.json.tag.PassList'>, <class 'flask.json.tag.TagBytes'>, <class 'flask.json.tag.TagMarkup'>, <class 'flask.json.tag.TagUUID'>, <class 'flask.json.tag.TagDateTime'>]
Tag classes to bind when creating the serializer. Other tags can be
added later using register().
dumps(value)
Tag the value and dump it to a compact JSON string.
loads(value)
Load data from a JSON string and deserialized any tagged objects.
register(tag_class, force=False, index=-1)
Register a new tag with this serializer.
- tag_class – tag class to register. Will be instantiated with this serializer instance.
- force – overwrite an existing tag. If false (default), a
KeyErroris raised. - index – index to insert the new tag in the tag order. Useful when the new tag is a special case of an existing tag. If -1 (default), the tag is appended to the end of the order.
force is
not true.tag(value)
Convert a value to a tagged representation if necessary.
untag(value)
Convert a tagged representation back to the original type.
class flask.json.tag.JSONTag(serializer)
Base class for defining type tags for TaggedJSONSerializer.
check(value)
Check if the given value should be tagged by this tag.
key = None
The tag to mark the serialized object with. If None, this tag is
only used as an intermediate step during tagging.
tag(value)
Convert the value to a valid JSON type and add the tag structure around it.
to_json(value)
Convert the Python object to an object that is a valid JSON type. The tag will be added later.
to_python(value)
Convert the JSON representation back to the correct type. The tag will already be removed.
Let’s seen an example that adds support for OrderedDict.
Dicts don’t have an order in Python or JSON, so to handle this we will dump
the items as a list of [key, value] pairs. Subclass JSONTag and
give it the new key ' od' to identify the type. The session serializer
processes dicts first, so insert the new tag at the front of the order since
OrderedDict must be processed before dict.
from flask.json.tag import JSONTag
class TagOrderedDict(JSONTag):
__slots__ = ('serializer',)
key = ' od'
def check(self, value):
return isinstance(value, OrderedDict)
def to_json(self, value):
return [[k, self.serializer.tag(v)] for k, v in iteritems(value)]
def to_python(self, value):
return OrderedDict(value)
app.session_interface.serializer.register(TagOrderedDict, 0)
Template Rendering
flask.render_template(template_name_or_list, **context)
Renders a template from the template folder with the given context.
- template_name_or_list – the name of the template to be rendered, or an iterable with template names the first one existing will be rendered
- context – the variables that should be available in the context of the template.
flask.render_template_string(source, **context)
Renders a template from the given template source string with the given context. Template variables will be autoescaped.
- source – the source code of the template to be rendered
- context – the variables that should be available in the context of the template.
flask.get_template_attribute(template_name, attribute)
Loads a macro (or variable) a template exports. This can be used to
invoke a macro from within Python code. If you for example have a
template named _cider.html with the following contents:
{% macro hello(name) %}Hello {{ name }}!{% endmacro %}
You can access this from Python code like this:
hello = get_template_attribute('_cider.html', 'hello')
return hello('World')
New in version 0.2.
- template_name – the name of the template
- attribute – the name of the variable of macro to access
Configuration
class flask.Config(root_path, defaults=None)
Works exactly like a dict but provides ways to fill it from files or special dictionaries. There are two common patterns to populate the config.
Either you can fill the config from a config file:
app.config.from_pyfile('yourconfig.cfg')
Or alternatively you can define the configuration options in the
module that calls from_object() or provide an import path to
a module that should be loaded. It is also possible to tell it to
use the same module and with that provide the configuration values
just before the call:
DEBUG = True
SECRET_KEY = 'development key'
app.config.from_object(__name__)
In both cases (loading from any Python file or loading from modules), only uppercase keys are added to the config. This makes it possible to use lowercase values in the config file for temporary values that are not added to the config or to define the config keys in the same file that implements the application.
Probably the most interesting way to load configurations is from an environment variable pointing to a file:
app.config.from_envvar('YOURAPPLICATION_SETTINGS')
In this case before launching the application you have to set this environment variable to the file you want to use. On Linux and OS X use the export statement:
export YOURAPPLICATION_SETTINGS='/path/to/config/file'
On windows use [UNKNOWN NODE title_reference] instead.
- root_path – path to which files are read relative from. When the
config object is created by the application, this is
the application’s
root_path. - defaults – an optional dictionary of default values
from_envvar(variable_name, silent=False)
Loads a configuration from an environment variable pointing to a configuration file. This is basically just a shortcut with nicer error messages for this line of code:
app.config.from_pyfile(os.environ['YOURAPPLICATION_SETTINGS'])
- variable_name – name of the environment variable
- silent – set to
Trueif you want silent failure for missing files.
True if able to load config, False otherwise.from_json(filename, silent=False)
Updates the values in the config from a JSON file. This function
behaves as if the JSON object was a dictionary and passed to the
from_mapping() function.
- filename – the filename of the JSON file. This can either be an absolute filename or a filename relative to the root path.
- silent – set to
Trueif you want silent failure for missing files.
New in version 0.11.
from_mapping(*mapping, **kwargs)
Updates the config like update() ignoring items with non-upper
keys.
New in version 0.11.
from_object(obj)
Updates the values from the given object. An object can be of one of the following two types:
- a string: in this case the object with that name will be imported
- an actual object reference: that object is used directly
Objects are usually either modules or classes. from_object()
loads only the uppercase attributes of the module/class. A dict
object will not work with from_object() because the keys of a
dict are not attributes of the dict class.
Example of module-based configuration:
app.config.from_object('yourapplication.default_config')
from yourapplication import default_config
app.config.from_object(default_config)
You should not use this function to load the actual configuration but
rather configuration defaults. The actual config should be loaded
with from_pyfile() and ideally from a location not within the
package because the package might be installed system wide.
See Development / Production for an example of class-based configuration
using from_object().
from_pyfile(filename, silent=False)
Updates the values in the config from a Python file. This function
behaves as if the file was imported as module with the
from_object() function.
- filename – the filename of the config. This can either be an absolute filename or a filename relative to the root path.
- silent – set to
Trueif you want silent failure for missing files.
New in version 0.7: [UNKNOWN NODE title_reference] parameter.
get_namespace(namespace, lowercase=True, trim_namespace=True)
Returns a dictionary containing a subset of configuration options that match the specified namespace/prefix. Example usage:
app.config['IMAGE_STORE_TYPE'] = 'fs'
app.config['IMAGE_STORE_PATH'] = '/var/app/images'
app.config['IMAGE_STORE_BASE_URL'] = 'http://img.website.com'
image_store_config = app.config.get_namespace('IMAGE_STORE_')
The resulting dictionary [UNKNOWN NODE title_reference] would look like:
{
'type': 'fs',
'path': '/var/app/images',
'base_url': 'http://img.website.com'
}
This is often useful when configuration options map directly to keyword arguments in functions or class constructors.
- namespace – a configuration namespace
- lowercase – a flag indicating if the keys of the resulting dictionary should be lowercase
- trim_namespace – a flag indicating if the keys of the resulting dictionary should not include the namespace
New in version 0.11.
Stream Helpers
flask.stream_with_context(generator_or_function)
Request contexts disappear when the response is started on the server. This is done for efficiency reasons and to make it less likely to encounter memory leaks with badly written WSGI middlewares. The downside is that if you are using streamed responses, the generator cannot access request bound information any more.
This function however can help you keep the context around for longer:
from flask import stream_with_context, request, Response
@app.route('/stream')
def streamed_response():
@stream_with_context
def generate():
yield 'Hello '
yield request.args['name']
yield '!'
return Response(generate())
Alternatively it can also be used around a specific generator:
from flask import stream_with_context, request, Response
@app.route('/stream')
def streamed_response():
def generate():
yield 'Hello '
yield request.args['name']
yield '!'
return Response(stream_with_context(generate()))
New in version 0.9.
Useful Internals
class flask.ctx.RequestContext(app, environ, request=None)
The request context contains all request relevant information. It is created at the beginning of the request and pushed to the [UNKNOWN NODE title_reference] and removed at the end of it. It will create the URL adapter and request object for the WSGI environment provided.
Do not attempt to use this class directly, instead use
test_request_context() and
request_context() to create this object.
When the request context is popped, it will evaluate all the
functions registered on the application for teardown execution
(teardown_request()).
The request context is automatically popped at the end of the request
for you. In debug mode the request context is kept around if
exceptions happen so that interactive debuggers have a chance to
introspect the data. With 0.4 this can also be forced for requests
that did not fail and outside of DEBUG mode. By setting
'flask._preserve_context' to True on the WSGI environment the
context will not pop itself at the end of the request. This is used by
the test_client() for example to implement the
deferred cleanup functionality.
You might find this helpful for unittests where you need the
information from the context local around for a little longer. Make
sure to properly pop() the stack yourself in
that situation, otherwise your unittests will leak memory.
copy()
Creates a copy of this request context with the same request object. This can be used to move a request context to a different greenlet. Because the actual request object is the same this cannot be used to move a request context to a different thread unless access to the request object is locked.
New in version 0.10.
match_request()
Can be overridden by a subclass to hook into the matching of the request.
pop(exc=<object object>)
Pops the request context and unbinds it by doing that. This will
also trigger the execution of functions registered by the
teardown_request() decorator.
Changed in version 0.9: Added the [UNKNOWN NODE title_reference] argument.
push()
Binds the request context to the current context.
flask._request_ctx_stack
The internal LocalStack that is used to implement
all the context local objects used in Flask. This is a documented
instance and can be used by extensions and application code but the
use is discouraged in general.
The following attributes are always present on each layer of the stack:
- [UNKNOWN NODE title_reference]
- the active Flask application.
- [UNKNOWN NODE title_reference]
- the URL adapter that was used to match the request.
- [UNKNOWN NODE title_reference]
- the current request object.
- [UNKNOWN NODE title_reference]
- the active session object.
- [UNKNOWN NODE title_reference]
- an object with all the attributes of the
flask.gobject. - [UNKNOWN NODE title_reference]
- an internal cache for the flashed messages.
Example usage:
from flask import _request_ctx_stack
def get_session():
ctx = _request_ctx_stack.top
if ctx is not None:
return ctx.session
class flask.ctx.AppContext(app)
The application context binds an application object implicitly
to the current thread or greenlet, similar to how the
RequestContext binds request information. The application
context is also implicitly created if a request context is created
but the application is not on top of the individual application
context.
pop(exc=<object object>)
Pops the app context.
push()
Binds the app context to the current context.
flask._app_ctx_stack
Works similar to the request context but only binds the application. This is mainly there for extensions to store data.
New in version 0.9.
class flask.blueprints.BlueprintSetupState(blueprint, app, options, first_registration)
Temporary holder object for registering a blueprint with the
application. An instance of this class is created by the
make_setup_state() method and later passed
to all register callback functions.
add_url_rule(rule, endpoint=None, view_func=None, **options)
A helper method to register a rule (and optionally a view function) to the application. The endpoint is automatically prefixed with the blueprint’s name.
app = None
a reference to the current application
blueprint = None
a reference to the blueprint that created this setup state.
first_registration = None
as blueprints can be registered multiple times with the application and not everything wants to be registered multiple times on it, this attribute can be used to figure out if the blueprint was registered in the past already.
options = None
a dictionary with all options that were passed to the
register_blueprint() method.
subdomain = None
The subdomain that the blueprint should be active for, None
otherwise.
url_defaults = None
A dictionary with URL defaults that is added to each and every URL that was defined with the blueprint.
Signals
New in version 0.6.
signals.signals_available
True if the signaling system is available. This is the case
when blinker is installed.
The following signals exist in Flask:
flask.template_rendered
This signal is sent when a template was successfully rendered. The signal is invoked with the instance of the template as [UNKNOWN NODE title_reference] and the context as dictionary (named [UNKNOWN NODE title_reference]).
Example subscriber:
def log_template_renders(sender, template, context, **extra):
sender.logger.debug('Rendering template "%s" with context %s',
template.name or 'string template',
context)
from flask import template_rendered
template_rendered.connect(log_template_renders, app)
flask.before_render_template
This signal is sent before template rendering process. The signal is invoked with the instance of the template as [UNKNOWN NODE title_reference] and the context as dictionary (named [UNKNOWN NODE title_reference]).
Example subscriber:
def log_template_renders(sender, template, context, **extra):
sender.logger.debug('Rendering template "%s" with context %s',
template.name or 'string template',
context)
from flask import before_render_template
before_render_template.connect(log_template_renders, app)
flask.request_started
This signal is sent when the request context is set up, before
any request processing happens. Because the request context is already
bound, the subscriber can access the request with the standard global
proxies such as request.
Example subscriber:
def log_request(sender, **extra):
sender.logger.debug('Request context is set up')
from flask import request_started
request_started.connect(log_request, app)
flask.request_finished
This signal is sent right before the response is sent to the client. It is passed the response to be sent named [UNKNOWN NODE title_reference].
Example subscriber:
def log_response(sender, response, **extra):
sender.logger.debug('Request context is about to close down. '
'Response: %s', response)
from flask import request_finished
request_finished.connect(log_response, app)
flask.got_request_exception
This signal is sent when an exception happens during request processing. It is sent before the standard exception handling kicks in and even in debug mode, where no exception handling happens. The exception itself is passed to the subscriber as [UNKNOWN NODE title_reference].
Example subscriber:
def log_exception(sender, exception, **extra):
sender.logger.debug('Got exception during processing: %s', exception)
from flask import got_request_exception
got_request_exception.connect(log_exception, app)
flask.request_tearing_down
This signal is sent when the request is tearing down. This is always called, even if an exception is caused. Currently functions listening to this signal are called after the regular teardown handlers, but this is not something you can rely on.
Example subscriber:
def close_db_connection(sender, **extra):
session.close()
from flask import request_tearing_down
request_tearing_down.connect(close_db_connection, app)
As of Flask 0.9, this will also be passed an [UNKNOWN NODE title_reference] keyword argument that has a reference to the exception that caused the teardown if there was one.
flask.appcontext_tearing_down
This signal is sent when the app context is tearing down. This is always called, even if an exception is caused. Currently functions listening to this signal are called after the regular teardown handlers, but this is not something you can rely on.
Example subscriber:
def close_db_connection(sender, **extra):
session.close()
from flask import appcontext_tearing_down
appcontext_tearing_down.connect(close_db_connection, app)
This will also be passed an [UNKNOWN NODE title_reference] keyword argument that has a reference to the exception that caused the teardown if there was one.
flask.appcontext_pushed
This signal is sent when an application context is pushed. The sender is the application. This is usually useful for unittests in order to temporarily hook in information. For instance it can be used to set a resource early onto the [UNKNOWN NODE title_reference] object.
Example usage:
from contextlib import contextmanager
from flask import appcontext_pushed
@contextmanager
def user_set(app, user):
def handler(sender, **kwargs):
g.user = user
with appcontext_pushed.connected_to(handler, app):
yield
And in the testcode:
def test_user_me(self):
with user_set(app, 'john'):
c = app.test_client()
resp = c.get('/users/me')
assert resp.data == 'username=john'
New in version 0.10.
flask.appcontext_popped
This signal is sent when an application context is popped. The sender
is the application. This usually falls in line with the
appcontext_tearing_down signal.
New in version 0.10.
flask.message_flashed
This signal is sent when the application is flashing a message. The messages is sent as [UNKNOWN NODE title_reference] keyword argument and the category as [UNKNOWN NODE title_reference].
Example subscriber:
recorded = []
def record(sender, message, category, **extra):
recorded.append((message, category))
from flask import message_flashed
message_flashed.connect(record, app)
New in version 0.10.
class signals.Namespace
An alias for blinker.base.Namespace if blinker is available,
otherwise a dummy class that creates fake signals. This class is
available for Flask extensions that want to provide the same fallback
system as Flask itself.
signal(name, doc=None)
Creates a new signal for this namespace if blinker is available,
otherwise returns a fake signal that has a send method that will
do nothing but will fail with a RuntimeError for all other
operations, including connecting.
Class-Based Views
New in version 0.7.
class flask.views.View
Alternative way to use view functions. A subclass has to implement
dispatch_request() which is called with the view arguments from
the URL routing system. If methods is provided the methods
do not have to be passed to the add_url_rule()
method explicitly:
class MyView(View):
methods = ['GET']
def dispatch_request(self, name):
return 'Hello %s!' % name
app.add_url_rule('/hello/<name>', view_func=MyView.as_view('myview'))
When you want to decorate a pluggable view you will have to either do that
when the view function is created (by wrapping the return value of
as_view()) or you can use the decorators attribute:
class SecretView(View):
methods = ['GET']
decorators = [superuser_required]
def dispatch_request(self):
...
The decorators stored in the decorators list are applied one after another when the view function is created. Note that you can not use the class based decorators since those would decorate the view class and not the generated view function!
classmethod as_view(name, *class_args, **class_kwargs)
Converts the class into an actual view function that can be used
with the routing system. Internally this generates a function on the
fly which will instantiate the View on each request and call
the dispatch_request() method on it.
The arguments passed to as_view() are forwarded to the
constructor of the class.
decorators = ()
The canonical way to decorate class-based views is to decorate the return value of as_view(). However since this moves parts of the logic from the class declaration to the place where it’s hooked into the routing system.
You can place one or more decorators in this list and whenever the view function is created the result is automatically decorated.
New in version 0.8.
dispatch_request()
Subclasses have to override this method to implement the actual view function code. This method is called with all the arguments from the URL rule.
methods = None
A list of methods this view can handle.
provide_automatic_options = None
Setting this disables or force-enables the automatic options handling.
class flask.views.MethodView
A class-based view that dispatches request methods to the corresponding
class methods. For example, if you implement a get method, it will be
used to handle GET requests.
class CounterAPI(MethodView):
def get(self):
return session.get('counter', 0)
def post(self):
session['counter'] = session.get('counter', 0) + 1
return 'OK'
app.add_url_rule('/counter', view_func=CounterAPI.as_view('counter'))
dispatch_request(*args, **kwargs)
Subclasses have to override this method to implement the actual view function code. This method is called with all the arguments from the URL rule.
URL Route Registrations
Generally there are three ways to define rules for the routing system:
- You can use the
flask.Flask.route()decorator. - You can use the
flask.Flask.add_url_rule()function. - You can directly access the underlying Werkzeug routing system
which is exposed as
flask.Flask.url_map.
Variable parts in the route can be specified with angular brackets
(/user/<username>). By default a variable part in the URL accepts any
string without a slash however a different converter can be specified as
well by using <converter:name>.
Variable parts are passed to the view function as keyword arguments.
The following converters are available:
| [UNKNOWN NODE title_reference] | accepts any text without a slash (the default) |
| [UNKNOWN NODE title_reference] | accepts integers |
| [UNKNOWN NODE title_reference] | like [UNKNOWN NODE title_reference] but for floating point values |
| [UNKNOWN NODE title_reference] | like the default but also accepts slashes |
| [UNKNOWN NODE title_reference] | matches one of the items provided |
| [UNKNOWN NODE title_reference] | accepts UUID strings |
Custom converters can be defined using flask.Flask.url_map.
Here are some examples:
@app.route('/')
def index():
pass
@app.route('/<username>')
def show_user(username):
pass
@app.route('/post/<int:post_id>')
def show_post(post_id):
pass
An important detail to keep in mind is how Flask deals with trailing slashes. The idea is to keep each URL unique so the following rules apply:
- If a rule ends with a slash and is requested without a slash by the user, the user is automatically redirected to the same page with a trailing slash attached.
- If a rule does not end with a trailing slash and the user requests the page with a trailing slash, a 404 not found is raised.
This is consistent with how web servers deal with static files. This also makes it possible to use relative link targets safely.
You can also define multiple rules for the same function. They have to be unique however. Defaults can also be specified. Here for example is a definition for a URL that accepts an optional page:
@app.route('/users/', defaults={'page': 1})
@app.route('/users/page/<int:page>')
def show_users(page):
pass
This specifies that /users/ will be the URL for page one and
/users/page/N will be the URL for page [UNKNOWN NODE title_reference].
Here are the parameters that route() and
add_url_rule() accept. The only difference is that
with the route parameter the view function is defined with the decorator
instead of the [UNKNOWN NODE title_reference] parameter.
| [UNKNOWN NODE title_reference] | the URL rule as string |
| [UNKNOWN NODE title_reference] | the endpoint for the registered URL rule. Flask itself assumes that the name of the view function is the name of the endpoint if not explicitly stated. |
| [UNKNOWN NODE title_reference] | the function to call when serving a request to the
provided endpoint. If this is not provided one can
specify the function later by storing it in the
view_functions dictionary with the
endpoint as key. |
| [UNKNOWN NODE title_reference] | A dictionary with defaults for this rule. See the example above for how defaults work. |
| [UNKNOWN NODE title_reference] | specifies the rule for the subdomain in case subdomain matching is in use. If not specified the default subdomain is assumed. |
| [UNKNOWN NODE title_reference] | the options to be forwarded to the underlying
Rule object. A change to
Werkzeug is handling of method options. methods is a list
of methods this rule should be limited to (GET, POST
etc.). By default a rule just listens for GET (and
implicitly HEAD). Starting with Flask 0.6, OPTIONS is
implicitly added and handled by the standard request
handling. They have to be specified as keyword arguments. |
View Function Options
For internal usage the view functions can have some attributes attached to
customize behavior the view function would normally not have control over.
The following attributes can be provided optionally to either override
some defaults to add_url_rule() or general behavior:
- [UNKNOWN NODE title_reference]: The name of a function is by default used as endpoint. If endpoint is provided explicitly this value is used. Additionally this will be prefixed with the name of the blueprint by default which cannot be customized from the function itself.
- [UNKNOWN NODE title_reference]: If methods are not provided when the URL rule is added, Flask will look on the view function object itself if a [UNKNOWN NODE title_reference] attribute exists. If it does, it will pull the information for the methods from there.
- [UNKNOWN NODE title_reference]: if this attribute is set Flask will
either force enable or disable the automatic implementation of the
HTTP
OPTIONSresponse. This can be useful when working with decorators that want to customize theOPTIONSresponse on a per-view basis. - [UNKNOWN NODE title_reference]: if this attribute is set, Flask will always add
these methods when registering a URL rule even if the methods were
explicitly overridden in the
route()call.
Full example:
def index():
if request.method == 'OPTIONS':
# custom options handling here
...
return 'Hello World!'
index.provide_automatic_options = False
index.methods = ['GET', 'OPTIONS']
app.add_url_rule('/', index)
New in version 0.8: The [UNKNOWN NODE title_reference] functionality was added.
Command Line Interface
class flask.cli.FlaskGroup(add_default_commands=True, create_app=None, add_version_option=True, load_dotenv=True, **extra)
Special subclass of the AppGroup group that supports
loading more commands from the configured Flask app. Normally a
developer does not have to interface with this class but there are
some very advanced use cases for which it makes sense to create an
instance of this.
For information as of why this is useful see Custom Scripts.
- add_default_commands – if this is True then the default run and shell commands wil be added.
- add_version_option – adds the
--versionoption. - create_app – an optional callback that is passed the script info and returns the loaded app.
- load_dotenv – Load the nearest
.envand.flaskenvfiles to set environment variables. Will also change the working directory to the directory containing the first file found.
Changed in version 1.0: If installed, python-dotenv will be used to load environment variables
from .env and .flaskenv files.
get_command(ctx, name)
Given a context and a command name, this returns a
Command object if it exists or returns [UNKNOWN NODE title_reference].
list_commands(ctx)
Returns a list of subcommand names in the order they should appear.
main(*args, **kwargs)
This is the way to invoke a script with all the bells and
whistles as a command line application. This will always terminate
the application after a call. If this is not wanted, SystemExit
needs to be caught.
This method is also available by directly calling the instance of
a Command.
New in version 3.0: Added the [UNKNOWN NODE title_reference] flag to control the standalone mode.
- args – the arguments that should be used for parsing. If not
provided,
sys.argv[1:]is used. - prog_name – the program name that should be used. By default
the program name is constructed by taking the file
name from
sys.argv[0]. - complete_var – the environment variable that controls the
bash completion support. The default is
"_<prog_name>_COMPLETE"with prog name in uppercase. - standalone_mode – the default behavior is to invoke the script
in standalone mode. Click will then
handle exceptions and convert them into
error messages and the function will never
return but shut down the interpreter. If
this is set to [UNKNOWN NODE title_reference] they will be
propagated to the caller and the return
value of this function is the return value
of
invoke(). - extra – extra keyword arguments are forwarded to the context
constructor. See
Contextfor more information.
class flask.cli.AppGroup(name=None, commands=None, **attrs)
This works similar to a regular click Group but it
changes the behavior of the command() decorator so that it
automatically wraps the functions in with_appcontext().
Not to be confused with FlaskGroup.
command(*args, **kwargs)
This works exactly like the method of the same name on a regular
click.Group but it wraps callbacks in with_appcontext()
unless it’s disabled by passing with_appcontext=False.
group(*args, **kwargs)
This works exactly like the method of the same name on a regular
click.Group but it defaults the group class to
AppGroup.
class flask.cli.ScriptInfo(app_import_path=None, create_app=None)
Help object to deal with Flask applications. This is usually not
necessary to interface with as it’s used internally in the dispatching
to click. In future versions of Flask this object will most likely play
a bigger role. Typically it’s created automatically by the
FlaskGroup but you can also manually create it and pass it
onwards as click object.
app_import_path = None
Optionally the import path for the Flask application.
create_app = None
Optionally a function that is passed the script info to create the instance of the application.
data = None
A dictionary with arbitrary data that can be associated with this script info.
load_app()
Loads the Flask app (if not yet loaded) and returns it. Calling this multiple times will just result in the already loaded app to be returned.
flask.cli.load_dotenv(path=None)
Load “dotenv” files in order of precedence to set environment variables.
If an env var is already set it is not overwritten, so earlier files in the list are preferred over later files.
Changes the current working directory to the location of the first file found, with the assumption that it is in the top level project directory and will be where the Python path should import local packages from.
This is a no-op if python-dotenv is not installed.
True if a file was loaded.New in version 1.0.
flask.cli.with_appcontext(f)
Wraps a callback so that it’s guaranteed to be executed with the
script’s application context. If callbacks are registered directly
to the app.cli object then they are wrapped with this function
by default unless it’s disabled.
flask.cli.pass_script_info(f)
Marks a function so that an instance of ScriptInfo is passed
as first argument to the click callback.
flask.cli.run_command = <click.core.Command object>
Run a local development server.
This server is for development purposes only. It does not provide the stability, security, or performance of production WSGI servers.
The reloader and debugger are enabled by default if FLASK_ENV=development or FLASK_DEBUG=1.
flask.cli.shell_command = <click.core.Command object>
Runs an interactive Python shell in the context of a given Flask application. The application will populate the default namespace of this shell according to it’s configuration.
This is useful for executing small snippets of management code without having to manually configure the application.