python3.x中arr [：] = []和arr [] = []之间的区别？

Question

这两行之间有什么区别：

arr[:] = []
arr = []

我知道他们两个清单。

Answer 1

对于第二个，我认为你的意思是arr = []。

不同之处在于， arr 指向新空列表，只是减少现有列表中的引用计数。

只有当其他东西指向原始列表时，区别才是重要的。

>>> 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]