Class Flask

src/flask/app.py:81–1536

The flask object implements a WSGI application and acts as the central object. It is passed the name of the module or package of the application. Once it is created it will act as a central registry for the view functions, the URL rules, template configuration and much more. The n

class Flask(App):
    """The flask object implements a WSGI application and acts as the central
    object.  It is passed the name of the module or package of the
    application.  Once it is created it will act as a central registry for
    the view functions, the URL rules, template configuration and much more.

    The name of the package is used to resolve resources from inside the
    package or the folder the module is contained in depending on if the
    package parameter resolves to an actual python package (a folder with
    an :file:`__init__.py` file inside) or a standard module (just a ``.py`` file).

    For more information about resource loading, see :func:`open_resource`.

    Usually you create a :class:`Flask` instance in your main module or
    in the :file:`__init__.py` file of your package like this::

        from flask import Flask
        app = Flask(__name__)

    .. admonition:: About the First Parameter

        The idea of the first parameter is to give Flask an idea of what
        belongs to your application.  This name is used to find resources
        on the filesystem, can be used by extensions to improve debugging
        information and a lot more.

        So it's important what you provide there.  If you are using a single
        module, `__name__` is always the correct value.  If you however are
        using a package, it's usually recommended to hardcode the name of
        your package there.

        For example if your application is defined in :file:`yourapplication/app.py`
        you should create it with one of the two versions below::

            app = Flask('yourapplication')
            app = Flask(__name__.split('.')[0])

        Why is that?  The application will work even with `__name__`, thanks
        to how resources are looked up.  However it will make debugging more
        painful.  Certain extensions can make assumptions based on the
        import name of your application.  For example the Flask-SQLAlchemy
        extension will look for the code in your application that triggered
        an SQL query in debug mode.  If the import name is not properly set
        up, that debugging information is lost.  (For example it would only
        pick up SQL queries in `yourapplication.app` and not
        `yourapplication.views.frontend`)

    .. versionadded:: 0.7
       The `static_url_path`, `static_folder`, and `template_folder`
       parameters were added.

    .. versionadded:: 0.8
       The `instance_path` and `instance_relative_config` parameters were
       added.

    .. versionadded:: 0.11
       The `root_path` parameter was added.