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+.. _`entry_points`:
+
+============
+Entry Points
+============
+
+Packages may provide commands to be run at the console (console scripts),
+such as the ``pip`` command. These commands are defined for a package
+as a specific kind of entry point in the ``setup.cfg`` or
+``setup.py``.
+
+
+Console Scripts
+===============
+
+First consider an example without entry points. Imagine a package
+defined thus:
+
+.. code-block:: bash
+
+    timmins/
+        timmins/__init__.py
+        timmins/__main__.py
+        setup.cfg # or setup.py
+        #other necessary files
+
+with ``__init__.py`` as:
+
+.. code-block:: python
+
+    def hello_world():
+        print("Hello world")
+
+and ``__main__.py`` providing a hook:
+
+.. code-block:: python
+
+    from . import hello_world
+
+    if __name__ == '__main__':
+        hello_world()
+
+After installing the package, the function may be invoked through the
+`runpy <https://docs.python.org/3/library/runpy.html>`_ module:
+
+.. code-block:: bash
+
+    python -m timmins
+
+Adding a console script entry point allows the package to define a
+user-friendly name for installers of the package to execute. Installers
+like pip will create wrapper scripts to execute a function. In the
+above example, to create a command ``hello-world`` that invokes
+``timmins.hello_world``, add a console script entry point to
+``setup.cfg``:
+
+.. code-block:: ini
+
+    [options.entry_points]
+    console_scripts =
+        hello-world = timmins:hello_world
+
+After installing the package, a user may invoke that function by simply calling
+``hello-world`` on the command line.
+
+The syntax for entry points is specified as follows:
+
+.. code-block:: ini
+
+    <name> = [<package>.[<subpackage>.]]<module>[:<object>.<object>]
+
+where ``name`` is the name for the script you want to create, the left hand
+side of ``:`` is the module that contains your function and the right hand
+side is the object you want to invoke (e.g. a function).
+
+In addition to ``console_scripts``, Setuptools supports ``gui_scripts``, which
+will launch a GUI application without running in a terminal window.
+
+
+.. _dynamic discovery of services and plugins:
+
+Advertising Behavior
+====================
+
+Console scripts are one use of the more general concept of entry points. Entry
+points more generally allow a packager to advertise behavior for discovery by
+other libraries and applications. This feature enables "plug-in"-like
+functionality, where one library solicits entry points and any number of other
+libraries provide those entry points.
+
+A good example of this plug-in behavior can be seen in
+`pytest plugins <https://docs.pytest.org/en/latest/writing_plugins.html>`_,
+where pytest is a test framework that allows other libraries to extend
+or modify its functionality through the ``pytest11`` entry point.
+
+The console scripts work similarly, where libraries advertise their commands
+and tools like ``pip`` create wrapper scripts that invoke those commands.
+
+For a project wishing to solicit entry points, Setuptools recommends the
+`importlib.metadata <https://docs.python.org/3/library/importlib.metadata.html>`_
+module (part of stdlib since Python 3.8) or its backport,
+`importlib_metadata <https://pypi.org/project/importlib_metadata>`_.
+
+For example, to find the console script entry points from the example above:
+
+.. code-block:: pycon
+
+    >>> from importlib import metadata
+    >>> eps = metadata.entry_points()['console_scripts']
+
+``eps`` is now a list of ``EntryPoint`` objects, one of which corresponds
+to the ``hello-world = timmins:hello_world`` defined above. Each ``EntryPoint``
+contains the ``name``, ``group``, and ``value``. It also supplies a ``.load()``
+method to import and load that entry point (module or object).
+
+.. code-block:: ini
+
+    [options.entry_points]
+    my.plugins =
+        hello-world = timmins:hello_world
+
+Then, a different project wishing to load 'my.plugins' plugins could run
+the following routine to load (and invoke) such plugins:
+
+.. code-block:: pycon
+
+    >>> from importlib import metadata
+    >>> eps = metadata.entry_points()['my.plugins']
+    >>> for ep in eps:
+    ...     plugin = ep.load()
+    ...     plugin()
+    ...
+
+The project soliciting the entry points needs not to have any dependency
+or prior knowledge about the libraries implementing the entry points, and
+downstream users are able to compose functionality by pulling together
+libraries implementing the entry points.
+
+
+Dependency Management
+=====================
+
+Some entry points may require additional dependencies to properly function.
+For such an entry point, declare in square brackets any number of dependency
+``extras`` following the entry point definition. Such entry points will only
+be viable if their extras were declared and installed. See the
+:doc:`guide on dependencies management <dependency_management>` for
+more information on defining extra requirements. Consider from the
+above example:
+
+.. code-block:: ini
+
+    [options.entry_points]
+    console_scripts =
+        hello-world = timmins:hello_world [pretty-printer]
+
+In this case, the ``hello-world`` script is only viable if the ``pretty-printer``
+extra is indicated, and so a plugin host might exclude that entry point
+(i.e. not install a console script) if the relevant extra dependencies are not
+installed.