docs: def extract_rows(data, *rows):
      """Extract rows specified in the argument list.
  
  >>> chart_data.extract_rows([[10,20], [30,40], [50,60]], 1, 2)
  [[30,40],[50,60]]
  """
      try:
          # for python 2.2
          # return [data[r] for r in rows]
          out = []
          for r in rows:
              out.append(data[r])
          return out
      except IndexError:
          raise IndexError("data=%s rows=%s" % (data, rows))
      return out