code: def _get_kdjj(df, n_days):
          
          k_column = 'kdjk_{}'.format(n_days)
          d_column = 'kdjd_{}'.format(n_days)
          j_column = 'kdjj_{}'.format(n_days)
          df[j_column] = 3 * df[k_column] - 2 * df[d_column]
docs: Get the J of KDJ
  
          J = 3K-2D
          :param df: data
          :param n_days: calculation range
          :return: None