分配list [：] = […]时冒号在Python中做什么？

Question

我遇到以下代码：

# O(n) space       
def rotate(self, nums, k):
    deque = collections.deque(nums)
    k %= len(nums)
    for _ in xrange(k):
        deque.appendleft(deque.pop())
    nums[:] = list(deque) # <- Code in question

这是什么nums[:] =做nums =不？就此而言，那没有nums[:]做什么nums呢？

Answer 1

此语法是切片分配。一片[:]意味着整个列表。nums[:] =和之间的区别在于nums =后者不会替换原始列表中的元素。当有两个引用列表时，这是可见的

>>> original = [1, 2, 3]
>>> other = original
>>> original[:] = [0, 0] # changes the contents of the list that both
                         # original and other refer to 
>>> other # see below, now you can see the change through other
[0, 0]

要查看差异，只需[:]从上面的分配中删除。

>>> original = [1, 2, 3]
>>> other = original
>>> original = [0, 0] # original now refers to a different list than other
>>> other # other remains the same
[1, 2, 3]

从字面上看，如果list是变量名而不是内建函数，则将问题的标题替换为省略号

>>> list = [1,2,3,4]
>>> list[:] = [...]
>>> list
[Ellipsis]