Abstract Factory for Python
===========================

Copyright (c) 2016-2017 David Betz

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See test\_provider.py unit test for usage.

Basically an implementation of an abstract factory pattern.

In one system where I use this, I create factories for eachs type of
thing in my system. So, SearchFactory, CloudStorageFactory,
QueueFactory, AristotleFactory, etc... These would implement for ID
interface like ICloudStorageProvider (in Node, it's just a class).

Each of these would have their own switch/case (or whatever) to create
the factory for it. So, for example, I may have config in a YAML file
specifying that I want to use Mongo for my Aristotle provider
("Aristotle" is what most people incorrectly call "NoSQL").

To begin, create the factory (do this one for the entirety of your
system):

::

    abstractFactory = AbstractFactory()

Then, add your factories:

::

        abstractFactory.set(SearchFactory)
        abstractFactory.set(CloudStorageFactory)
        abstractFactory.set(QueueFactory)
        abstractFactory.set(AristotleFactory)

When the time comes, just ask for your provider:

::

    provider = abstractFactory.resolve(IAristotleProvider)

Your code SHOULD. NOT. CARE. ABOUT. MONGO. It should the your
configuration or something handle that. Don't tightly couple your
providers.

Also note that the resolver also accepts various arguments for extra
flexibility:

::

    provider = abstractFactory.resolve(IAristotleProvider, "alternateConnectionString", collection="log") 

Despite what random bloggers say, service locators are awesome and
provide excellent decoupling.

Look at the ``Mock`` examples provided with the tests; they're rather
extensive.

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