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.. _server:
Development Server
==================
.. currentmodule:: flask
Starting with Flask 0.11 there are multiple built-in ways to run a
development server. The best one is the :command:`flask` command line utility
but you can also continue using the :meth:`Flask.run` method.
Command Line
------------
The :command:`flask` command line script (:ref:`cli`) is strongly
recommended for development because it provides a superior reload
experience due to how it loads the application. The basic usage is like
this::
$ export FLASK_APP=my_application
$ export FLASK_ENV=development
$ flask run
This enables the development environment, including the interactive
debugger and reloader, and then starts the server on
*http://localhost:5000/*.
The individual features of the server can be controlled by passing more
arguments to the ``run`` option. For instance the reloader can be
disabled::
$ flask run --no-reload
.. note::
Prior to Flask 1.0 the :envvar:`FLASK_ENV` environment variable was
not supported and you needed to enable debug mode by exporting
``FLASK_DEBUG=1``. This can still be used to control debug mode, but
you should prefer setting the development environment as shown
above.
In Code
-------
The alternative way to start the application is through the
:meth:`Flask.run` method. This will immediately launch a local server
exactly the same way the :command:`flask` script does.
Example::
if __name__ == '__main__':
app.run()
This works well for the common case but it does not work well for
development which is why from Flask 0.11 onwards the :command:`flask`
method is recommended. The reason for this is that due to how the reload
mechanism works there are some bizarre side-effects (like executing
certain code twice, sometimes crashing without message or dying when a
syntax or import error happens).
It is however still a perfectly valid method for invoking a non automatic
reloading application.
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