More KWARGS!
============

Motivation
----------

Extensive use of dependency injection, plus managing the configuration
for each of the components being injected, can result in some
spectacularly complex system configuration. One way to reduce the
complexity is to use configuration templates that contain useful
defaults, and simply overwrite the properties that need to be changed
for the new configuration. ``@override`` has been created to provide
this templating system for Python function calls (primarily class
constructors).

``@override`` will decorate a function to accept a ``kwargs`` parameter
which is just like ``**kwargs``, but the call parameters will override
the properties in ``kwargs``, rather than raise duplicate key
exceptions.

**Example**

We decorate the ``login()`` function with ``@override``. In this case,
``username`` is a required parameter, and ``password`` will default to
``None``. The kwargs parameter should always default to ``None`` so that
it's not required.

::

        @override
        def login(username, password=None, kwargs=None):
            pass

Define some ``dicts`` for use with our ``kwargs`` parameter:

::

        creds = {"userame": "ekyle", "password": "password123"}
        alt_creds = {"username": "klahnakoski"}

The simplest case is when we use kwargs with no overrides

::

        login(kwargs=creds)
        # SAME AS
        login(**creds)
        # SAME AS
        login(username="ekyle", password="password123")

You may override any property in kwargs: In this case it is ``password``

::

        login(password="123", kwargs=creds)
        # SAME AS
        login(username="ekyle", password="123")

There is no problem with overriding everything in ``kwargs``:

::

        login(username="klahnakoski", password="asd213", kwargs=creds)
        # SAME AS
        login(username="klahnakoski", password="asd213")

You may continue to use ``**kwargs``; which provides a way to overlay
one parameter template (``creds``) with another (``alt_creds``)

::

        login(kwargs=creds, **alt_creds)
        # SAME AS
        login(username="klahnakoski", password="password123")

