Retrieves a collection class from the cache, if available.

        :param service_name: The service a given ``Collection`` talks to. Ex.
            ``sqs``, ``sns``, ``dynamodb``, etc.
        :type service_name: string

        :param collection_name: The name of the ``Collection``. Ex.
            ``QueueCollection``, ``NotificationCollection``,
            ``TableCollection``, etc.
        :type collection_name: string

        :param base_class: (Optional) The base class of the object. Prevents
            "magically" loading the wrong class (one with a different base).
            Default is ``default``.
        :type base_class: class

        :returns: A <kotocore.collections.Collection> subclass

def get_collection(self, service_name, collection_name, base_class=None):
        """
        Retrieves a collection class from the cache, if available.

        :param service_name: The service a given ``Collection`` talks to. Ex.
            ``sqs``, ``sns``, ``dynamodb``, etc.
        :type service_name: string

        :param collection_name: The name of the ``Collection``. Ex.
            ``QueueCollection``, ``NotificationCollection``,
            ``TableCollection``, etc.
        :type collection_name: string

        :param base_class: (Optional) The base class of the object. Prevents
            "magically" loading the wrong class (one with a different base).
            Default is ``default``.
        :type base_class: class

        :returns: A <kotocore.collections.Collection> subclass
        """
        classpath = self.build_classpath(base_class)
        service = self.services.get(service_name, {})
        collections = service.get('collections', {})
        collection_options = collections.get(collection_name, {})
        collection_class = collection_options.get(classpath, None)

        if not collection_class:
            msg = "Collection '{0}' for {1} is not present in the cache."
            raise NotCached(msg.format(
                collection_name,
                service_name
            ))

        return collection_class