code: def get_timestamp(str_len=13):
      
      if isinstance(str_len, integer_types) and 0 < str_len < 17:
          return builtin_str(time.time()).replace(".", "")[:str_len]
  
      raise ParamsError("timestamp length can only between 0 and 16.")
docs: get timestamp string, length can only between 0 and 16