'Converts a list of v1 Keys to a list of v3 References.
Args:
v1_keys: a list of googledatastore.Key objects
Returns:
a list of entity_pb.Reference objects'

def v1_to_v3_references(self, v1_keys):

    v3_refs = []
    for v1_key in v1_keys:
        v3_ref = entity_pb.Reference()
        self.v1_to_v3_reference(v1_key, v3_ref)
        v3_refs.append(v3_ref)
    return v3_refs
