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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 get_path(self, wd):
 """ Returns the path associated to WD, if WD is unknown it returns None. @param wd: Watch descriptor. @type wd: int @return: Path or None. @rtype: string or None """

        watch_ = self._wmd.get(wd)
        if watch_ is not None:
            return watch_.path