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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 _next_dir_gen(self, root):
 """Generator for next directory element in the document. Args: root: root element in the XML tree. Yields: GCSFileStat for the next directory. """

    for e in root.getiterator(common._T_COMMON_PREFIXES):
      yield common.GCSFileStat(
          self._path + '/' + e.find(common._T_PREFIX).text,
          st_size=None, etag=None, st_ctime=None, is_dir=True)
      e.clear()
    yield None