global variable not assigned, newbie question

[Jean-Daniel Gamache]

Hi! here's a python newbie question ...
why is my variable (myNum) not assigned the value 10 ???

========

myNum = 0

def setNum():
    myNum = 10
    print myNum
    
def main():
    setNum()
    print myNum

if __name__ == '__main__':
    main()