.. _access-packaging-metadata:

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Accessing Briefcase packaging metadata at runtime
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When Briefcase installs your app, it adds a `PEP566
<https://peps.python.org/pep-0566/>`__ metadata file containing information
about your app, and Briefcase itself. You can retrieve this information at
runtime using the `Python builtin library 'importlib.metadata'
<https://docs.python.org/3/library/importlib.metadata.html>`__.
``importlib.metadata`` was added in Python 3.8; however, it has been backported
and published on PyPI as `'importlib_metadata'
<https://pypi.org/project/importlib-metadata/>`__ for older versions of Python.

To access application metadata at runtime, you can use the following code::

    import sys
    try:
        from importlib import metadata as importlib_metadata
    except ImportError:
        # Backwards compatibility - importlib.metadata was added in Python 3.8
        import importlib_metadata

    # Find the name of the module that was used to start the app
    app_module = sys.modules['__main__'].__package__
    # Retrieve the app's metadata
    metadata = importlib_metadata.metadata(app_module)

The ``metadata`` returned by this code will be a dictionary-like object that
contains the following identifying keys:

  * **Metadata-Version** - The syntax version of the metadata file itself (as
    defined in `PEP566 <https://peps.python.org/pep-0566/>`__).

  * **Briefcase-Version** - The version of Briefcase used to package the app.
    The existence of this key in app metadata can be used to identify if your
    application code is running in a Briefcase container; it will only exist if
    the app has been packaged by Briefcase.

It will also have the following keys, derived from your application's
``pyproject.toml`` configuration:

  * **Name** - :attr:`app_name`
  * **Formal-Name** - :attr:`formal_name`
  * **App-ID** - :attr:`bundle` and :attr:`app_name`, joined with a ``.``
  * **Version** - :attr:`version`
  * **Summary** - :attr:`description`

The metadata may also contain the following keys, if they have been defined
in your app's ``pyproject.toml`` configuration:

  * **Home-page** - :attr:`url`
  * **Author** - :attr:`author`
  * **Author-email** - :attr:`author_email`

For example, the metadata for the app constructed by the `BeeWare Tutorial
<https://docs.beeware.org/en/latest/tutorial/tutorial-1.html>`_ would
contain::

    Metadata-Version: 2.1
    Briefcase-Version: 0.3.1
    Name: helloworld
    Formal-Name: Hello World
    App-ID: com.example.helloworld
    Version: 0.0.1
    Home-page: https://example.com/helloworld
    Author: Jane Developer
    Author-email: jane@example.com
    Summary: My first application