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