Python Version
We recommend using the latest version of Python 3. Flask supports Python 3.4 and newer, Python 2.7, and PyPy.
Dependencies
These distributions will be installed automatically when installing Flask.
- Werkzeug implements WSGI, the standard Python interface between applications and servers.
- Jinja is a template language that renders the pages your application serves.
- MarkupSafe comes with Jinja. It escapes untrusted input when rendering templates to avoid injection attacks.
- ItsDangerous securely signs data to ensure its integrity. This is used to protect Flask’s session cookie.
- Click is a framework for writing command line applications. It provides
the
flask
command and allows adding custom management commands.
Optional dependencies
These distributions will not be installed automatically. Flask will detect and use them if you install them.
- Blinker provides support for Signals.
- SimpleJSON is a fast JSON implementation that is compatible with
Python’s
json
module. It is preferred for JSON operations if it is installed. - python-dotenv enables support for Environment Variables From dotenv when running
flask
commands. - Watchdog provides a faster, more efficient reloader for the development server.
Virtual environments
Use a virtual environment to manage the dependencies for your project, both in development and in production.
What problem does a virtual environment solve? The more Python projects you have, the more likely it is that you need to work with different versions of Python libraries, or even Python itself. Newer versions of libraries for one project can break compatibility in another project.
Virtual environments are independent groups of Python libraries, one for each project. Packages installed for one project will not affect other projects or the operating system’s packages.
Python 3 comes bundled with the venv
module to create virtual
environments. If you’re using a modern version of Python, you can continue on
to the next section.
If you’re using Python 2, see Install virtualenv first.
Create an environment
Create a project folder and a venv
folder within:
mkdir myproject
cd myproject
python3 -m venv venv
On Windows:
py -3 -m venv venv
If you needed to install virtualenv because you are on an older version of Python, use the following command instead:
virtualenv venv
On Windows:
\Python27\Scripts\virtualenv.exe venv
Activate the environment
Before you work on your project, activate the corresponding environment:
. venv/bin/activate
On Windows:
venv\Scripts\activate
Your shell prompt will change to show the name of the activated environment.
Install Flask
Within the activated environment, use the following command to install Flask:
pip install Flask
Living on the edge
If you want to work with the latest Flask code before it’s released, install or update the code from the master branch:
pip install -U https://github.com/pallets/flask/archive/master.tar.gz
Install virtualenv
If you are using Python 2, the venv module is not available. Instead, install virtualenv.
On Linux, virtualenv is provided by your package manager:
# Debian, Ubuntu
sudo apt-get install python-virtualenv
# CentOS, Fedora
sudo yum install python-virtualenv
# Arch
sudo pacman -S python-virtualenv
If you are on Mac OS X or Windows, download get-pip.py, then:
sudo python2 Downloads/get-pip.py
sudo python2 -m pip install virtualenv
On Windows, as an administrator:
\Python27\python.exe Downloads\get-pip.py
\Python27\python.exe -m pip install virtualenv
Now you can continue to Create an environment.