python - 为什么 somelist[len(somelist)] 生成一个 IndexError 而不是 somelist[len(somelist) :]?

Question

我知道 somelist[len(somelist)] 无法访问定义列表之外的索引 - 这是有道理的。

但是为什么 Python 允许你做 somelist[len(somelist):]？

我什至读过 somelist[len(somelist):] = [1] 等同于 somelist.append(1)

但为什么切片符号会改变索引“len(somelist)”仍然在列表范围之外的事实？

Answer 1

这是来自 documentation 的内容.任何可迭代对象的切片都有特定的规则；特别值得注意的是#4，强调我的:

The slice of s from i to j is defined as the sequence of items with index k such that i <= k < j. If i or j is greater than len(s), use len(s). If i is omitted or None, use 0. If j is omitted or None, use len(s). If i is greater than or equal to j, the slice is empty.