'Internal helper to turn an entity into an EntityProto protobuf.'

def _to_pb(self, pb=None, allow_partial=False, set_key=True):

    if (not allow_partial):
        self._check_initialized()
    if (pb is None):
        pb = entity_pb.EntityProto()
    if set_key:
        self._key_to_pb(pb)
    for (unused_name, prop) in sorted(self._properties.iteritems()):
        prop._serialize(self, pb, projection=self._projection)
    return pb
