.. currentmodule:: flask

Command Line Interface¶

Installing Flask installs the flask script, a Click_ command line interface, in your virtualenv. Executed from the terminal, this script gives access to built-in, extension, and application-defined commands. The --help option will give more information about any commands and options.

.. _Click: http://click.pocoo.org/

Application Discovery¶

The flask command is installed by Flask, not your application; it must be told where to find your application in order to use it. The FLASK_APP environment variable is used to specify how to load the application.

Unix Bash (Linux, Mac, etc.)::

$ export FLASK_APP=hello
$ flask run

Windows CMD::

&gt; set FLASK_APP=hello
&gt; flask run

Windows PowerShell::

&gt; $env:FLASK_APP = "hello"
&gt; flask run

While FLASK_APP supports a variety of options for specifying your application, most use cases should be simple. Here are the typical values:

(nothing) The file :file:wsgi.py is imported, automatically detecting an app (app). This provides an easy way to create an app from a factory with extra arguments.

FLASK_APP=hello The name is imported, automatically detecting an app (app) or factory (create_app).

FLASK_APP has three parts: an optional path that sets the current working directory, a Python file or dotted import path, and an optional variable name of the instance or factory. If the name is a factory, it can optionally be followed by arguments in parentheses. The following values demonstrate these parts:

FLASK_APP=src/hello Sets the current working directory to src then imports hello.

FLASK_APP=hello.web Imports the path hello.web.

FLASK_APP=hello:app2 Uses the app2 Flask instance in hello.

FLASK_APP="hello:create_app('dev')" The create_app factory in hello is called with the string 'dev' as the argument.

If FLASK_APP is not set, the command will look for a file called :file:wsgi.py or :file:app.py and try to detect an application instance or factory.

Within the given import, the command looks for an application instance named app or application, then any application instance. If no instance is found, the command looks for a factory function named create_app or make_app that returns an instance.

When calling an application factory, if the factory takes an argument named script_info, then the :class:~cli.ScriptInfo instance is passed as a keyword argument. If the application factory takes only one argument and no parentheses follow the factory name, the :class:~cli.ScriptInfo instance is passed as a positional argument. If parentheses follow the factory name, their contents are parsed as Python literals and passes as arguments to the function. This means that strings must still be in quotes.

Run the Development Server¶

The :func:run <cli.run_command> command will start the development server. It replaces the :meth:Flask.run method in most cases. ::

$ flask run
 * Serving Flask app "hello"
 * Running on http://127.0.0.1:5000/ (Press CTRL+C to quit)

.. warning:: Do not use this command to run your application in production. Only use the development server during development. The development server is provided for convenience, but is not designed to be particularly secure, stable, or efficient. See :ref:deployment for how to run in production.

Open a Shell¶

To explore the data in your application, you can start an interactive Python shell with the :func:shell <cli.shell_command> command. An application context will be active, and the app instance will be imported. ::

$ flask shell
Python 3.6.2 (default, Jul 20 2017, 03:52:27)
[GCC 7.1.1 20170630] on linux
App: example
Instance: /home/user/Projects/hello/instance
&gt;&gt;&gt;

Use :meth:~Flask.shell_context_processor to add other automatic imports.

Environments¶

.. versionadded:: 1.0

The environment in which the Flask app runs is set by the :envvar:FLASK_ENV environment variable. If not set it defaults to production. The other recognized environment is development. Flask and extensions may choose to enable behaviors based on the environment.

If the env is set to development, the flask command will enable debug mode and flask run will enable the interactive debugger and reloader.

::

$ FLASK_ENV=development flask run
 * Serving Flask app "hello"
 * Environment: development
 * Debug mode: on
 * Running on http://127.0.0.1:5000/ (Press CTRL+C to quit)
 * Restarting with inotify reloader
 * Debugger is active!
 * Debugger PIN: 223-456-919

Debug Mode¶

Debug mode will be enabled when :envvar:FLASK_ENV is development, as described above. If you want to control debug mode separately, use :envvar:FLASK_DEBUG. The value 1 enables it, 0 disables it.

Environment Variables From dotenv¶

Rather than setting FLASK_APP each time you open a new terminal, you can use Flask's dotenv support to set environment variables automatically.

If python-dotenv_ is installed, running the flask command will set environment variables defined in the files :file:.env and :file:.flaskenv. This can be used to avoid having to set FLASK_APP manually every time you open a new terminal, and to set configuration using environment variables similar to how some deployment services work.

Variables set on the command line are used over those set in :file:.env, which are used over those set in :file:.flaskenv. :file:.flaskenv should be used for public variables, such as FLASK_APP, while :file:.env should not be committed to your repository so that it can set private variables.

Directories are scanned upwards from the directory you call flask from to locate the files. The current working directory will be set to the location of the file, with the assumption that that is the top level project directory.

The files are only loaded by the flask command or calling :meth:~Flask.run. If you would like to load these files when running in production, you should call :func:~cli.load_dotenv manually.

.. _python-dotenv: https://github.com/theskumar/python-dotenv#readme

Setting Command Options

Click is configured to load default values for command options from
environment variables. The variables use the pattern
``FLASK_COMMAND_OPTION``. For example, to set the port for the run
command, instead of ``flask run --port 8000``:

.. code-block:: none

    $ export FLASK_RUN_PORT=8000
    $ flask run
     * Running on http://127.0.0.1:8000/

These can be added to the ``.flaskenv`` file just like ``FLASK_APP`` to
control default command options.


Disable dotenv
~~~~~~~~~~~~~~

The ``flask`` command will show a message if it detects dotenv files but
python-dotenv is not installed.

.. code-block:: none

    $ flask run
     * Tip: There are .env files present. Do "pip install python-dotenv" to use them.

You can tell Flask not to load dotenv files even when python-dotenv is
installed by setting the ``FLASK_SKIP_DOTENV`` environment variable.
This can be useful if you want to load them manually, or if you're using
a project runner that loads them already. Keep in mind that the
environment variables must be set before the app loads or it won't
configure as expected.

.. code-block:: none

    $ export FLASK_SKIP_DOTENV=1
    $ flask run


Environment Variables From virtualenv
-------------------------------------

If you do not want to install dotenv support, you can still set environment
variables by adding them to the end of the virtualenv's :file:`activate`
script. Activating the virtualenv will set the variables.

Unix Bash, :file:`venv/bin/activate`::

    $ export FLASK_APP=hello

Windows CMD, :file:`venv\\Scripts\\activate.bat`::

    > set FLASK_APP=hello

It is preferred to use dotenv support over this, since :file:`.flaskenv` can be
committed to the repository so that it works automatically wherever the project
is checked out.


Custom Commands
---------------

The ``flask`` command is implemented using `Click`_. See that project's
documentation for full information about writing commands.

This example adds the command ``create_user`` that takes the argument
``name``. ::

    import click
    from flask import Flask

    app = Flask(__name__)

    @app.cli.command()
    @click.argument('name')
    def create_user(name):
        ...

::

    $ flask create_user admin

This example adds the same command, but as ``user create``, a command in a
group. This is useful if you want to organize multiple related commands. ::

    import click
    from flask import Flask
    from flask.cli import AppGroup

    app = Flask(__name__)
    user_cli = AppGroup('user')

    @user_cli.command('create')
    @click.argument('name')
    def create_user(name):
        ...

    app.cli.add_command(user_cli)

::

    $ flask user create demo

See :ref:`testing-cli` for an overview of how to test your custom
commands.


Application Context
~~~~~~~~~~~~~~~~~~~

Commands added using the Flask app's :attr:`~Flask.cli`
:meth:`~cli.AppGroup.command` decorator will be executed with an application
context pushed, so your command and extensions have access to the app and its
configuration. If you create a command using the Click :func:`~click.command`
decorator instead of the Flask decorator, you can use
:func:`~cli.with_appcontext` to get the same behavior. ::

    import click
    from flask.cli import with_appcontext

    @click.command()
    @with_appcontext
    def do_work():
        ...

    app.cli.add_command(do_work)

If you're sure a command doesn't need the context, you can disable it::

    @app.cli.command(with_appcontext=False)
    def do_work():
        ...


Plugins
-------

Flask will automatically load commands specified in the ``flask.commands``
`entry point`_. This is useful for extensions that want to add commands when
they are installed. Entry points are specified in :file:`setup.py` ::

    from setuptools import setup

    setup(
        name='flask-my-extension',
        ...,
        entry_points={
            'flask.commands': [
                'my-command=flask_my_extension.commands:cli'
            ],
        },
    )


.. _entry point: https://packaging.python.org/tutorials/distributing-packages/#entry-points

Inside :file:`flask_my_extension/commands.py` you can then export a Click
object::

    import click

    @click.command()
    def cli():
        ...

Once that package is installed in the same virtualenv as your Flask project,
you can run ``flask my-command`` to invoke the command.


.. _custom-scripts:

Custom Scripts
--------------

When you are using the app factory pattern, it may be more convenient to define
your own Click script. Instead of using ``FLASK_APP`` and letting Flask load
your application, you can create your own Click object and export it as a
`console script`_ entry point.

Create an instance of :class:`~cli.FlaskGroup` and pass it the factory::

    import click
    from flask import Flask
    from flask.cli import FlaskGroup

    def create_app():
        app = Flask('wiki')
        # other setup
        return app

    @click.group(cls=FlaskGroup, create_app=create_app)
    def cli():
        """Management script for the Wiki application."""

Define the entry point in :file:`setup.py`::

    from setuptools import setup

    setup(
        name='flask-my-extension',
        ...,
        entry_points={
            'console_scripts': [
                'wiki=wiki:cli'
            ],
        },
    )

Install the application in the virtualenv in editable mode and the custom
script is available. Note that you don't need to set ``FLASK_APP``. ::

    $ pip install -e .
    $ wiki run

.. admonition:: Errors in Custom Scripts

    When using a custom script, if you introduce an error in your
    module-level code, the reloader will fail because it can no longer
    load the entry point.

    The ``flask`` command, being separate from your code, does not have
    this issue and is recommended in most cases.

.. _console script: https://packaging.python.org/tutorials/distributing-packages/#console-scripts


PyCharm Integration
-------------------

Prior to PyCharm 2018.1, the Flask CLI features weren't yet fully
integrated into PyCharm. We have to do a few tweaks to get them working
smoothly. These instructions should be similar for any other IDE you
might want to use.

In PyCharm, with your project open, click on *Run* from the menu bar and
go to *Edit Configurations*. You'll be greeted by a screen similar to
this:

.. image:: _static/pycharm-runconfig.png
    :align: center
    :class: screenshot
    :alt: screenshot of pycharm's run configuration settings

There's quite a few options to change, but once we've done it for one
command, we can easily copy the entire configuration and make a single
tweak to give us access to other commands, including any custom ones you
may implement yourself.

Click the + (*Add New Configuration*) button and select *Python*. Give
the configuration a good descriptive name such as "Run Flask Server".
For the ``flask run`` command, check "Single instance only" since you
can't run the server more than once at the same time.

Select *Module name* from the dropdown (**A**) then input ``flask``.

The *Parameters* field (**B**) is set to the CLI command to execute
(with any arguments). In this example we use ``run``, which will run
the development server.

You can skip this next step if you're using :ref:`dotenv`. We need to
add an environment variable (**C**) to identify our application. Click
on the browse button and add an entry with ``FLASK_APP`` on the left and
the Python import or file on the right (``hello`` for example).

Next we need to set the working directory (**D**) to be the folder where
our application resides.

If you have installed your project as a package in your virtualenv, you
may untick the *PYTHONPATH* options (**E**). This will more accurately
match how you deploy the app later.

Click *Apply* to save the configuration, or *OK* to save and close the
window. Select the configuration in the main PyCharm window and click
the play button next to it to run the server.

Now that we have a configuration which runs ``flask run`` from within
PyCharm, we can copy that configuration and alter the *Script* argument
to run a different CLI command, e.g. ``flask shell``.