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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 close(self):
 """ Close this SSHClient and its underlying `.Transport`. .. warning:: Failure to do this may, in some situations, cause your Python interpreter to hang at shutdown (often due to race conditions). It's good practice to `close` your client objects anytime you're done using them, instead of relying on garbage collection. """

        if self._transport is None:
            return
        self._transport.close()
        self._transport = None

        if self._agent is not None:
            self._agent.close()
            self._agent = None