a=Nonefor i in a:    print(‘zheli de i shi %d‘ % i)

报错： TypeError: ‘NoneType‘ object is not iterable

除非你提供你自己的return语句，每个函数都在结尾暗含有return None语句。

关于DocString：

def testing(x):    ‘‘‘This is a test function.This is a great feature.You must learn how to use this.‘‘‘    print(‘Your input is ‘,x)print(testing.__doc__)testing(18)testing(5)help(testing)



输出：

This is a test function.

This is a great feature.You must learn how to use this.
(‘Your input is ‘, 18)
(‘Your input is ‘, 5)
Help on function testing in module __main__:

testing(x)
This is a test function.

This is a great feature.You must learn how to use this.