def _rel_create_dict(relationships):
    """ Convert a set of :class:`.Relationship` objects into a dictionary
    of :class:`.Relationship` lists, keyed by type.

    :param relationships:
    :return:
    """
    d = {}
    for relationship in relationships:
        key = type(relationship).__name__
        d.setdefault(key, []).append(relationship)
    return d