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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _add_write_pbs(self, write_pbs):
 """Add `Write`` protobufs to this transaction. Args: write_pbs (List[google.cloud.proto.firestore.v1beta1.\ write_pb2.Write]):
 A list of write protobufs to be added. Raises: ValueError: If this transaction is read-only. """

        if self._read_only:
            raise ValueError(_WRITE_READ_ONLY)

        super(Transaction, self)._add_write_pbs(write_pbs)