logging.handlers --- Logging handlers[UNKNOWN NODE sidebar]Source code: Lib/logging/handlers.py
[UNKNOWN NODE transition]The following useful handlers are provided in the package. Note that three of
the handlers (StreamHandler, FileHandler and
NullHandler) are actually defined in the logging module itself,
but have been documented here along with the other handlers.
The StreamHandler class, located in the core logging package,
sends logging output to streams such as sys.stdout, sys.stderr or any
file-like object (or, more precisely, any object which supports write()
and flush() methods).
class logging.StreamHandler(stream=None)[source]
Returns a new instance of the StreamHandler class. If stream is
specified, the instance will use it for logging output; otherwise, sys.stderr
will be used.
emit(record)[source]
If a formatter is specified, it is used to format the record. The record
is then written to the stream with a newline terminator. If exception
information is present, it is formatted using
traceback.print_exception() and appended to the stream.
flush()[source]
Flushes the stream by calling its flush() method. Note that the
close() method is inherited from Handler and so
does no output, so an explicit flush() call may be needed at times.
The FileHandler class, located in the core logging package,
sends logging output to a disk file. It inherits the output functionality from
StreamHandler.
class logging.FileHandler(filename, mode='a', encoding=None, delay=False)[source]
Returns a new instance of the FileHandler class. The specified file is
opened and used as the stream for logging. If mode is not specified,
'a' is used. If encoding is not None, it is used to open the file
with that encoding. If delay is true, then file opening is deferred until the
first call to emit(). By default, the file grows indefinitely.
Changed in version 2.6: delay was added.
close()[source]
Closes the file.
emit(record)[source]
Outputs the record to the file.
New in version 2.7.
The NullHandler class, located in the core logging package,
does not do any formatting or output. It is essentially a 'no-op' handler
for use by library developers.
class logging.NullHandler[source]
Returns a new instance of the NullHandler class.
emit(record)[source]
This method does nothing.
handle(record)[source]
This method does nothing.
createLock()[source]
This method returns None for the lock, since there is no
underlying I/O to which access needs to be serialized.
See Configuring Logging for a Library for more information on how to use
NullHandler.
New in version 2.6.
The WatchedFileHandler class, located in the logging.handlers
module, is a FileHandler which watches the file it is logging to. If
the file changes, it is closed and reopened using the file name.
A file change can happen because of usage of programs such as newsyslog and logrotate which perform log file rotation. This handler, intended for use under Unix/Linux, watches the file to see if it has changed since the last emit. (A file is deemed to have changed if its device or inode have changed.) If the file has changed, the old file stream is closed, and the file opened to get a new stream.
This handler is not appropriate for use under Windows, because under Windows
open log files cannot be moved or renamed - logging opens the files with
exclusive locks - and so there is no need for such a handler. Furthermore,
ST_INO is not supported under Windows; stat() always returns zero
for this value.
class logging.handlers.WatchedFileHandler(filename[, mode[, encoding[, delay]]])[source]
Returns a new instance of the WatchedFileHandler class. The specified
file is opened and used as the stream for logging. If mode is not specified,
'a' is used. If encoding is not None, it is used to open the file
with that encoding. If delay is true, then file opening is deferred until the
first call to emit(). By default, the file grows indefinitely.
emit(record)[source]
Outputs the record to the file, but first checks to see if the file has changed. If it has, the existing stream is flushed and closed and the file opened again, before outputting the record to the file.
The RotatingFileHandler class, located in the logging.handlers
module, supports rotation of disk log files.
class logging.handlers.RotatingFileHandler(filename, mode='a', maxBytes=0, backupCount=0, encoding=None, delay=0)[source]
Returns a new instance of the RotatingFileHandler class. The specified
file is opened and used as the stream for logging. If mode is not specified,
'a' is used. If encoding is not None, it is used to open the file
with that encoding. If delay is true, then file opening is deferred until the
first call to emit(). By default, the file grows indefinitely.
You can use the maxBytes and backupCount values to allow the file to
rollover at a predetermined size. When the size is about to be exceeded,
the file is closed and a new file is silently opened for output. Rollover occurs
whenever the current log file is nearly maxBytes in length; if either of
maxBytes or backupCount is zero, rollover never occurs. If backupCount
is non-zero, the system will save old log files by appending the extensions
'.1', '.2' etc., to the filename. For example, with a backupCount of 5 and
a base file name of app.log, you would get app.log,
app.log.1, app.log.2, up to app.log.5. The file being
written to is always app.log. When this file is filled, it is closed
and renamed to app.log.1, and if files app.log.1,
app.log.2, etc. exist, then they are renamed to app.log.2,
app.log.3 etc. respectively.
Changed in version 2.6: delay was added.
doRollover()[source]
Does a rollover, as described above.
emit(record)
Outputs the record to the file, catering for rollover as described previously.
The TimedRotatingFileHandler class, located in the
logging.handlers module, supports rotation of disk log files at certain
timed intervals.
class logging.handlers.TimedRotatingFileHandler(filename, when='h', interval=1, backupCount=0, encoding=None, delay=False, utc=False)[source]
Returns a new instance of the TimedRotatingFileHandler class. The
specified file is opened and used as the stream for logging. On rotating it also
sets the filename suffix. Rotating happens based on the product of when and
interval.
You can use the when to specify the type of interval. The list of possible values is below. Note that they are not case sensitive.
| Value | Type of interval |
|---|---|
'S' | Seconds |
'M' | Minutes |
'H' | Hours |
'D' | Days |
'W0'-'W6' | Weekday (0=Monday) |
'midnight' | Roll over at midnight |
When using weekday-based rotation, specify 'W0' for Monday, 'W1' for Tuesday, and so on up to 'W6' for Sunday. In this case, the value passed for interval isn't used.
The system will save old log files by appending extensions to the filename.
The extensions are date-and-time based, using the strftime format
%Y-%m-%d_%H-%M-%S or a leading portion thereof, depending on the
rollover interval.
When computing the next rollover time for the first time (when the handler is created), the last modification time of an existing log file, or else the current time, is used to compute when the next rotation will occur.
If the utc argument is true, times in UTC will be used; otherwise local time is used.
If backupCount is nonzero, at most backupCount files will be kept, and if more would be created when rollover occurs, the oldest one is deleted. The deletion logic uses the interval to determine which files to delete, so changing the interval may leave old files lying around.
If delay is true, then file opening is deferred until the first call to
emit().
Changed in version 2.6: delay and utc were added.
doRollover()[source]
Does a rollover, as described above.
emit(record)
Outputs the record to the file, catering for rollover as described above.
The SocketHandler class, located in the logging.handlers module,
sends logging output to a network socket. The base class uses a TCP socket.
class logging.handlers.SocketHandler(host, port)[source]
Returns a new instance of the SocketHandler class intended to
communicate with a remote machine whose address is given by host and port.
close()[source]
Closes the socket.
emit()[source]
Pickles the record's attribute dictionary and writes it to the socket in
binary format. If there is an error with the socket, silently drops the
packet. If the connection was previously lost, re-establishes the
connection. To unpickle the record at the receiving end into a
LogRecord, use the makeLogRecord()
function.
handleError()[source]
Handles an error which has occurred during emit(). The most likely
cause is a lost connection. Closes the socket so that we can retry on the
next event.
makeSocket()[source]
This is a factory method which allows subclasses to define the precise
type of socket they want. The default implementation creates a TCP socket
(socket.SOCK_STREAM).
makePickle(record)[source]
Pickles the record's attribute dictionary in binary format with a length prefix, and returns it ready for transmission across the socket.
Note that pickles aren't completely secure. If you are concerned about security, you may want to override this method to implement a more secure mechanism. For example, you can sign pickles using HMAC and then verify them on the receiving end, or alternatively you can disable unpickling of global objects on the receiving end.
send(packet)[source]
Send a pickled string packet to the socket. This function allows for partial sends which can happen when the network is busy.
createSocket()[source]
Tries to create a socket; on failure, uses an exponential back-off algorithm. On initial failure, the handler will drop the message it was trying to send. When subsequent messages are handled by the same instance, it will not try connecting until some time has passed. The default parameters are such that the initial delay is one second, and if after that delay the connection still can't be made, the handler will double the delay each time up to a maximum of 30 seconds.
This behaviour is controlled by the following handler attributes:
retryStart(initial delay, defaulting to 1.0 seconds).retryFactor(multiplier, defaulting to 2.0).retryMax(maximum delay, defaulting to 30.0 seconds).
This means that if the remote listener starts up after the handler has been used, you could lose messages (since the handler won't even attempt a connection until the delay has elapsed, but just silently drop messages during the delay period).
The DatagramHandler class, located in the logging.handlers
module, inherits from SocketHandler to support sending logging messages
over UDP sockets.
class logging.handlers.DatagramHandler(host, port)[source]
Returns a new instance of the DatagramHandler class intended to
communicate with a remote machine whose address is given by host and port.
emit()
Pickles the record's attribute dictionary and writes it to the socket in
binary format. If there is an error with the socket, silently drops the
packet. To unpickle the record at the receiving end into a
LogRecord, use the makeLogRecord()
function.
makeSocket()[source]
The factory method of SocketHandler is here overridden to create
a UDP socket (socket.SOCK_DGRAM).
send(s)[source]
Send a pickled string to a socket.
The SysLogHandler class, located in the logging.handlers module,
supports sending logging messages to a remote or local Unix syslog.
class logging.handlers.SysLogHandler(address=('localhost', SYSLOG_UDP_PORT), facility=LOG_USER, socktype=socket.SOCK_DGRAM)[source]
Returns a new instance of the SysLogHandler class intended to
communicate with a remote Unix machine whose address is given by address in
the form of a (host, port) tuple. If address is not specified,
('localhost', 514) is used. The address is used to open a socket. An
alternative to providing a (host, port) tuple is providing an address as a
string, for example '/dev/log'. In this case, a Unix domain socket is used to
send the message to the syslog. If facility is not specified,
LOG_USER is used. The type of socket opened depends on the
socktype argument, which defaults to socket.SOCK_DGRAM and thus
opens a UDP socket. To open a TCP socket (for use with the newer syslog
daemons such as rsyslog), specify a value of socket.SOCK_STREAM.
Note that if your server is not listening on UDP port 514,
SysLogHandler may appear not to work. In that case, check what
address you should be using for a domain socket - it's system dependent.
For example, on Linux it's usually '/dev/log' but on OS/X it's
'/var/run/syslog'. You'll need to check your platform and use the
appropriate address (you may need to do this check at runtime if your
application needs to run on several platforms). On Windows, you pretty
much have to use the UDP option.
Changed in version 2.7: socktype was added.
close()[source]
Closes the socket to the remote host.
emit(record)[source]
The record is formatted, and then sent to the syslog server. If exception information is present, it is not sent to the server.
encodePriority(facility, priority)[source]
Encodes the facility and priority into an integer. You can pass in strings or integers - if strings are passed, internal mapping dictionaries are used to convert them to integers.
The symbolic LOG_ values are defined in SysLogHandler and
mirror the values defined in the sys/syslog.h header file.
Priorities
| Name (string) | Symbolic value |
|---|---|
alert | LOG_ALERT |
crit or critical | LOG_CRIT |
debug | LOG_DEBUG |
emerg or panic | LOG_EMERG |
err or error | LOG_ERR |
info | LOG_INFO |
notice | LOG_NOTICE |
warn or warning | LOG_WARNING |
Facilities
| Name (string) | Symbolic value |
|---|---|
auth | LOG_AUTH |
authpriv | LOG_AUTHPRIV |
cron | LOG_CRON |
daemon | LOG_DAEMON |
ftp | LOG_FTP |
kern | LOG_KERN |
lpr | LOG_LPR |
mail | LOG_MAIL |
news | LOG_NEWS |
syslog | LOG_SYSLOG |
user | LOG_USER |
uucp | LOG_UUCP |
local0 | LOG_LOCAL0 |
local1 | LOG_LOCAL1 |
local2 | LOG_LOCAL2 |
local3 | LOG_LOCAL3 |
local4 | LOG_LOCAL4 |
local5 | LOG_LOCAL5 |
local6 | LOG_LOCAL6 |
local7 | LOG_LOCAL7 |
mapPriority(levelname)[source]
Maps a logging level name to a syslog priority name.
You may need to override this if you are using custom levels, or
if the default algorithm is not suitable for your needs. The
default algorithm maps DEBUG, INFO, WARNING, ERROR and
CRITICAL to the equivalent syslog names, and all other level
names to 'warning'.
The NTEventLogHandler class, located in the logging.handlers
module, supports sending logging messages to a local Windows NT, Windows 2000 or
Windows XP event log. Before you can use it, you need Mark Hammond's Win32
extensions for Python installed.
class logging.handlers.NTEventLogHandler(appname, dllname=None, logtype='Application')[source]
Returns a new instance of the NTEventLogHandler class. The appname is
used to define the application name as it appears in the event log. An
appropriate registry entry is created using this name. The dllname should give
the fully qualified pathname of a .dll or .exe which contains message
definitions to hold in the log (if not specified, 'win32service.pyd' is used
- this is installed with the Win32 extensions and contains some basic
placeholder message definitions. Note that use of these placeholders will make
your event logs big, as the entire message source is held in the log. If you
want slimmer logs, you have to pass in the name of your own .dll or .exe which
contains the message definitions you want to use in the event log). The
logtype is one of 'Application', 'System' or 'Security', and
defaults to 'Application'.
close()[source]
At this point, you can remove the application name from the registry as a source of event log entries. However, if you do this, you will not be able to see the events as you intended in the Event Log Viewer - it needs to be able to access the registry to get the .dll name. The current version does not do this.
emit(record)[source]
Determines the message ID, event category and event type, and then logs the message in the NT event log.
getEventCategory(record)[source]
Returns the event category for the record. Override this if you want to specify your own categories. This version returns 0.
getEventType(record)[source]
Returns the event type for the record. Override this if you want to
specify your own types. This version does a mapping using the handler's
typemap attribute, which is set up in __init__() to a dictionary
which contains mappings for DEBUG, INFO,
WARNING, ERROR and CRITICAL. If you are using
your own levels, you will either need to override this method or place a
suitable dictionary in the handler's typemap attribute.
getMessageID(record)[source]
Returns the message ID for the record. If you are using your own messages,
you could do this by having the msg passed to the logger being an ID
rather than a format string. Then, in here, you could use a dictionary
lookup to get the message ID. This version returns 1, which is the base
message ID in win32service.pyd.
The SMTPHandler class, located in the logging.handlers module,
supports sending logging messages to an email address via SMTP.
class logging.handlers.SMTPHandler(mailhost, fromaddr, toaddrs, subject, credentials=None, secure=None)[source]
Returns a new instance of the SMTPHandler class. The instance is
initialized with the from and to addresses and subject line of the email.
The toaddrs should be a list of strings. To specify a non-standard SMTP
port, use the (host, port) tuple format for the mailhost argument. If you
use a string, the standard SMTP port is used. If your SMTP server requires
authentication, you can specify a (username, password) tuple for the
credentials argument.
To specify the use of a secure protocol (TLS), pass in a tuple to the
secure argument. This will only be used when authentication credentials are
supplied. The tuple should be either an empty tuple, or a single-value tuple
with the name of a keyfile, or a 2-value tuple with the names of the keyfile
and certificate file. (This tuple is passed to the
smtplib.SMTP.starttls() method.)
Changed in version 2.6: credentials was added.
Changed in version 2.7: secure was added.
emit(record)[source]
Formats the record and sends it to the specified addressees.
getSubject(record)[source]
If you want to specify a subject line which is record-dependent, override this method.
The MemoryHandler class, located in the logging.handlers module,
supports buffering of logging records in memory, periodically flushing them to a
target handler. Flushing occurs whenever the buffer is full, or when an
event of a certain severity or greater is seen.
MemoryHandler is a subclass of the more general
BufferingHandler, which is an abstract class. This buffers logging
records in memory. Whenever each record is added to the buffer, a check is made
by calling shouldFlush() to see if the buffer should be flushed. If it
should, then flush() is expected to do the flushing.
class logging.handlers.BufferingHandler(capacity)[source]
Initializes the handler with a buffer of the specified capacity.
emit(record)[source]
Appends the record to the buffer. If shouldFlush() returns true,
calls flush() to process the buffer.
flush()[source]
You can override this to implement custom flushing behavior. This version just zaps the buffer to empty.
shouldFlush(record)[source]
Returns true if the buffer is up to capacity. This method can be overridden to implement custom flushing strategies.
class logging.handlers.MemoryHandler(capacity, flushLevel=ERROR, target=None)[source]
Returns a new instance of the MemoryHandler class. The instance is
initialized with a buffer size of capacity. If flushLevel is not specified,
ERROR is used. If no target is specified, the target will need to be
set using setTarget() before this handler does anything useful.
close()[source]
Calls flush(), sets the target to None and clears the
buffer.
flush()[source]
For a MemoryHandler, flushing means just sending the buffered
records to the target, if there is one. The buffer is also cleared when
this happens. Override if you want different behavior.
setTarget(target)[source]
Sets the target handler for this handler.
shouldFlush(record)[source]
Checks for buffer full or a record at the flushLevel or higher.
The HTTPHandler class, located in the logging.handlers module,
supports sending logging messages to a Web server, using either GET or
POST semantics.
class logging.handlers.HTTPHandler(host, url, method='GET')[source]
Returns a new instance of the HTTPHandler class. The host can be
of the form host:port, should you need to use a specific port number.
mapLogRecord(record)[source]
Provides a dictionary, based on record, which is to be URL-encoded
and sent to the web server. The default implementation just returns
record.__dict__. This method can be overridden if e.g. only a
subset of LogRecord is to be sent to the web server, or
if more specific customization of what's sent to the server is required.
emit(record)[source]
Sends the record to the Web server as a URL-encoded dictionary. The
mapLogRecord() method is used to convert the record to the
dictionary to be sent.
Note
Since preparing a record for sending it to a Web server is not
the same as a generic formatting operation, using setFormatter()
to specify a Formatter for a HTTPHandler has no effect.
Instead of calling format(), this handler calls mapLogRecord()
and then urllib.urlencode() to encode the dictionary in a form
suitable for sending to a Web server.
See also
- Module
logging - API reference for the logging module.
- Module
logging.config - Configuration API for the logging module.