code: def get_keys(data_list, leading_columns=LEADING_COLUMNS):
      all_keys = set().union(*(list(d.keys()) for d in data_list))
      leading_keys = []
      for key in leading_columns:
          if key not in all_keys:
              continue
          leading_keys.append(key)
          all_keys.remove(key)
      return leading_keys + sorted(all_keys)