def apply_doc(source):
    """
    Decorator that will prepend ``source``'s docstring to the decorated \
    object's docstring.

    :param source: Object with docstring to be prepended onto the decorated object.
    """

    def decorator(target):
        source_doc = source.__doc__

        if target.__doc__ is None:
            target.__doc__ = source_doc
        else:
            target.__doc__ = "\n".join((source_doc, target.__doc__))

        return target

    return decorator