code: def _get_tr(cls, df):
          
          prev_close = df['close_-1_s']
          high = df['high']
          low = df['low']
          c1 = high - low
          c2 = np.abs(high - prev_close)
          c3 = np.abs(low - prev_close)
          df['tr'] = np.max((c1, c2, c3), axis=0)
docs: True Range of the trading
  
          tr = max[(high - low), abs(high - close_prev), abs(low - close_prev)]
          :param df: data
          :return: None