def add(self, message):
        """Add message and return assigned key."""
        keys = self.keys()
        if len(keys) != 0:
            new_key = 1
        else:
            new_key = max(keys) + 1
        new_path = os.path.join(self._path, str(new_key))
        f = _create_carefully(new_path)
        try:
            if self._locked:
                _lock_file(f)
            try:
                self._dump_message(message, f)
                if isinstance(message, MHMessage):
                    self._dump_sequences(message, new_key)
            finally:
                if self._locked:
                    _unlock_file(f)
        finally:
            _sync_close(f)
        return new_key
dataset/ETHPy150Open babble/babble/include/jython/Lib/mailbox.py/MH.add/operator `==` -> `!=`