def serialize_model_base(obj, fields_method, model_method, fields=None,
    exclude=None, related=None, related_fields=None, parent='',
    use_natural_keys=False, handle_related=lambda x, y: y):
    """ Convert model instances to basic Python data types. """
    fields = fields_method(obj, fields=fields, exclude=exclude)
    related = related or {}
    related_fields = related_fields or {}
    return model_method(obj, fields, related, related_fields, parent,
        use_natural_keys, handle_related)
