Extensions are extra packages that add functionality to a Flask application. For example, an extension might add support for sending email or connecting to a database. Some extensions add entire new frameworks to help build certain types of applications, like a ReST API.
Flask extensions are usually named "Flask-Foo" or "Foo-Flask". Many extensions are listed in the Extension Registry, which can be updated by extension developers. You can also search PyPI for packages tagged with Framework :: Flask.
Consult each extension's documentation for installation, configuration, and usage instructions. Generally, extensions pull their own configuration from :attr:`app.config <flask.Flask.config>` and are passed an application instance during initialization. For example, an extension caled "Flask-Foo" might be used like this:
from flask_foo import Foo
foo = Foo()
app = Flask(__name__)
app.config.update(
FOO_BAR='baz',
FOO_SPAM='eggs',
)
foo.init_app(app)
While the Extension Registry contains many Flask extensions, you may not find an extension that fits your need. If this is the case, you can create your own. Read :ref:`extension-dev` to develop your own Flask extension.