'Converts a list of v4 Keys to a list of v3 References.
Args:
v4_keys: a list of entity_v4_pb.Key objects
Returns:
a list of entity_pb.Reference objects'

def v4_to_v3_references(self, v4_keys):

    v3_refs = []
    for v4_key in v4_keys:
        v3_ref = entity_pb.Reference()
        self.v4_to_v3_reference(v4_key, v3_ref)
        v3_refs.append(v3_ref)
    return v3_refs
