threading.Timer()

Question

i have to write a program in network course that is something like selective repeat but a need a timer. after search in google i found that threading.Timer can help me, i wrote a simple program just for test how threading.Timer work that was this:

import threading  def hello():     print "hello, world"  t = threading.Timer(10.0, hello) t.start()  print "Hi" i=10 i=i+20 print i 

this program run correctly. but when i try to define hello function in a way that give parameter like:

import threading  def hello(s):     print s  h="hello world" t = threading.Timer(10.0, hello(h)) t.start()  print "Hi" i=10 i=i+20 print i 

the out put is :

hello world Hi 30 Exception in thread Thread-1: Traceback (most recent call last):   File "/System/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/threading.py", line 522, in __bootstrap_inner     self.run()   File "/System/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/threading.py", line 726, in run     self.function(*self.args, **self.kwargs) TypeError: 'NoneType' object is not callable 

i cant understand what is the problem! can any one help me?

Answer 1

You just need to put the arguments to hello into a separate item in the function call, like this,

t = threading.Timer(10.0, hello, [h]) 

This is a common approach in Python. Otherwise, when you use Timer(10.0, hello(h)), the result of this function call is passed to Timer, which is None since hello doesn't make an explicit return.