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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 wait(self):
 """Wait on a task to finish and stop it when it has finished. Raises: RuntimeError: If the task hasn't been started or has already been stopped. Returns: The ``return_values`` of the task. """

        if self._status is not TaskStatus.STARTED:
            raise RuntimeError("Cannot wait on %s in state %s" %
                               (self, self._status))
        self._wait()
        self.stop()
        return self.return_values