docs: def _select1(data, field, depth, output):
      """
      SELECT A SINGLE FIELD
      """
      for d in data:
          for i, f in enumerate(field[depth:]):
              d = d[f]
              if d == None:
                  output.append(None)
                  break
              elif is_list(d):
                  _select1(d, field, i + 1, output)
                  break
          else:
              output.append(d)