python3.x中的arr [:] = []和arr [] = []之间的区别? [英] Difference between arr[:]=[] and arr[]=[] in python3.x?

问题描述

这两行之间是否有任何区别:

Is there any difference between these two lines:

arr[:] = []
arr = []

我知道他们两个都清楚了.

I know both of them clear list.

推荐答案

对于第二个问题，我认为您的意思是 arr = [] .

For the second one, I think you meant arr = [].

不同之处在于，它具有 arr 指向 new 空列表，只是减少了现有列表上的引用计数.

What that does differently is that it has arr point to a new empty list and just decrements the refcount on the existing list.

仅当其他内容指向原始列表时，差异才重要.

The difference is only important if something else is pointing to the original list.

>>> orig = [10, 20, 30]
>>> arr = orig              # Second reference to the same list.
>>> arr[:] = []             # Clears the one list, so that arr and orig are empty
>>> orig
[]

与之对比:

>>> orig = [10, 20, 30]
>>> arr = orig              # Second reference to the same list.
>>> arr = []                # Points arr to a new list, leaving orig unchanged
>>> orig
[10, 20, 30]

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