docs: def load_hdf(cls, filename, path=''):
          """
          Load TripleOrbitPopulation from saved .h5 file.
  
          :param filename:
              HDF file name.
  
          :param path:
              Path within HDF file where data is stored.
  
          """
          df_long = pd.read_hdf(filename,'{}/long/df'.format(path))
          df_short = pd.read_hdf(filename,'{}/short/df'.format(path))
          return cls.from_df(df_long, df_short)