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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 the environment."""

        # make sure the environment hasn't already been closed
        if self._env is None:
            raise ValueError('env has already been closed.')
        # purge the environment from C++ memory
        _LIB.Close(self._env)
        # deallocate the object locally
        self._env = None
        # if there is an image viewer open, delete it
        if self.viewer is not None:
            self.viewer.close()