python中[无]和[]之间有什么区别? [英] what is difference between [None] and [] in python?

问题描述

我认为[无]与[]相同，但是在我的测试中，也许有些东西...

I think [None] is same as [], but in my test , maybe there is something...

>>>print len([])
0
>>>print len([None])
1

我什么时候应该使用None?和[]

when should i use the None ? and []

和另一个有趣的问题

>>>c= []
>>>d= []
>>>print c is d
False
>>>a= 1
>>>b=1
print a is b
True

为什么空列表的ID授予不同?

why empty list's id granting that is different?

推荐答案

[] 是一个空列表

[无] 是具有一个元素的列表.那个元素是 None

[None] is a list with one element. That one element is None

是检查引用是否相等.如果两个对象通过 reference 引用同一对象，则 is 将返回true.

is checks for reference equality. If both objects refer to the same object by reference then is will return true.

a = []
b = a
a is [] #false
a is b  #true

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