docs: def is_pickle_file(abspath):
      """Parse file extension.
      
      - *.pickle: uncompressed, utf-8 encode pickle file
      - *.gz: compressed, utf-8 encode pickle file
      """
      abspath = abspath.lower()
      fname, ext = os.path.splitext(abspath)
      if ext in [".pickle", ".pk", ".p"]:
          is_pickle = True
      elif ext == ".gz":
          is_pickle = False
      elif ext == ".tmp":
          return is_pickle_file(fname)
      else:
          raise PickleExtError(
              "'%s' is not a valid pickle file. "
              "extension has to be '.pickle' for uncompressed, '.gz' "
              "for compressed." % abspath)
      return is_pickle