code: def _pathway_side_information(pathway_positive_series,
                                pathway_negative_series,
                                index):
      
      positive_series_label = pd.Series(["pos"] * len(pathway_positive_series))
      negative_series_label = pd.Series(["neg"] * len(pathway_negative_series))
      side_information = positive_series_label.append(
          negative_series_label)
      side_information.index = index
      side_information.name = "side"
      return side_information
docs: Create the pandas.Series containing the side labels that correspond
      to each pathway, based on the user-specified gene signature definition.