a=None

for 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.

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Python Special Syntax 2