<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def save(self):
 """Save the row back to the spreadsheet"""

        if self._sheet.readonly:
            raise ReadOnlyException
        if not self._changed:
            # nothing to save
            return
        gd_client = self._sheet.client
        assert gd_client is not None
        try:
            entry = gd_client.UpdateRow(self._entry, self._data)
        except RequestError as e:
            error_data = e.args[0]
            if error_data.status == 403:
                #  Forbidden
                raise
            if error_data.status == 409:
                # conflict
                raise
            else:
                raise
        self._entry = entry
        # reset `_changed` flag
        self._changed = False
        return entry