code: def get_path(self, wd):
          
          watch_ = self._wmd.get(wd)
          if watch_ is not None:
              return watch_.path
docs: 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