docs: def pickle_compress(obj, print_compression_info=False):
      """pickle and compress an object"""
      p = pickle.dumps(obj)
      c = zlib.compress(p)
      if print_compression_info:
          print ("len = {:,d} compr={:,d} ratio:{:.6f}".format(len(p), len(c), float(len(c))/len(p)))
      return c