code: def call_me(iocb):
      
      if _debug: call_me._debug("callback_function %r", iocb)
  
      # it will be successful or have an error
      print("call me, %r or %r" % (iocb.ioResponse, iocb.ioError))
docs: When a controller completes the processing of a request, 
      the IOCB can contain one or more functions to be called.