<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def cancel(self):
 """If last Operation's value of `done` is true, returns false; otherwise, issues OperationsClient.cancel_operation and returns true. """

        if self.done():
            return False

        self._client.cancel_operation(self._operation.name)
        return True