为什么函数以“返回0"结尾?而不是“返回"在python中?

问题描述：

能否请您解释返回0"和返回"之间的区别?例如:

Could you please explain the difference between "return 0" and "return"? For example:

do_1():
    for i in xrange(5):
        do_sth()
    return 0

do_2():
    for i in xrange(5):
        do_sth()
    return

以上两个功能有什么区别?

What is the difference between two functions above?

答

取决于用法:

>>> def ret_Nothing():
...     return
... 
>>> def ret_None():
...     return None
... 
>>> def ret_0():
...     return 0
... 
>>> ret_Nothing() == None
True
>>> ret_Nothing() is None  # correct way to compare values with None
True
>>> ret_None() is None
True
>>> ret_0() is None
False
>>> ret_0() == 0
True
>>> # and...
>>> repr(ret_Nothing())
'None'

并且如Tichodroma提到的， 0 不等于 None .但是，在布尔上下文中，它们都是 False :

And as mentioned by Tichodroma, 0 is not equal to None. However, in boolean context, they are both False:

>>> if ret_0():
...     print 'this will not be printed'
... else:
...     print '0 is boolean False'
... 
0 is boolean False
>>> if ret_None():
...     print 'this will not be printed'
... else:
...     print 'None is also boolean False'
... 
None is also boolean False

有关Python布尔上下文的更多信息:真值测试

More on Boolean context in Python: Truth Value Testing

为什么函数以“返回0"结尾?而不是“返回"在python中?

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