Python负零切片 [英] Python negative zero slicing

问题描述

我经常发现自己必须处理序列中的最后n个项目，其中n可能为0.问题是尝试使用 [-n:] 进行切片无法 n == 0 的情况，因此需要笨拙的特殊情况代码.例如

I often find myself having to work with the last n items in a sequence, where n may be 0. The problem is that trying to slice with [-n:] won't work in the case of n == 0, so awkward special case code is required. For example

if len(b): 
    assert(isAssignableSeq(env, self.stack[-len(b):], b))
    newstack = self.stack[:-len(b)] + a
else: #special code required if len=0 since slice[-0:] doesn't do what we want
    newstack = self.stack + a

我的问题是-有没有办法在不需要笨拙的特殊大小写的情况下获得此行为?如果我不必一直检查0，那么代码会简单得多.

My question is - is there any way to get this behavior without requiring the awkward special casing? The code would be much simpler if I didn't have to check for 0 all the time.

推荐答案

您可以将其从 L [-2:] 切换为 L [len(L)-2:]

>>> L = [1,2,3,4,5]
>>> L[len(L)-2:]
[4, 5]
>>> L[len(L)-0:]
[]

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