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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 manual_dir(self):
 """Returns the directory containing the manually extracted data."""

    if not tf.io.gfile.exists(self._manual_dir):
      raise AssertionError(
          'Manual directory {} does not exist. Create it and download/extract '
          'dataset artifacts in there.'.format(self._manual_dir))
    return self._manual_dir