python从字符串创建切片对象 [英] python create slice object from string

问题描述

我想从字符串创建切片对象;现在唯一的方法似乎通过一个繁琐的hacky评估声明

I'd like to create a slice object from a string; right now the only way seems through a cumbersome hacky eval statement

class getslice:
    def __getitem__(self, idx): return idx[0]
eval("getslice()[%s, 1]" %(":-1"))

提前感谢。

编辑：抱歉，如果原始提示不清楚，输入在这种情况下是：-1。关键在于解析字符串。 Ignacio Vazquez-Abrams的回答至少解决了这个问题（并且似乎也适用于反向索引），但我认为如果不是概念上干净的话，上面的解决方案仍然更加清晰（如果Python改变切片语法，它将正常工作）。 / p>

Edit: Sorry if the original prompt was not clear, the input in this case was ":-1". The point was to parse the string. Ignacio Vazquez-Abrams's response at least solved the problem (and seems to work with reverse indexing as well), but I think my solution above is still more clear if not conceptually clean (and will work correctly if Python ever changes slicing syntax).

推荐答案

slice(*[{True: lambda n: None, False: int}[x == ''](x) for x in (mystring.split(':') + ['', '', ''])[:3]])

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