Python中的可变宽度后向问题 [英] Variable-Width Lookbehind Issue in Python

问题描述

我遇到以下情况:

1) car on the right shoulder
2) car on the left shoulder
3) car on the shoulder

我想在不存在left | right的情况下匹配"shoulder".因此只有3)返回肩膀"

I want to match "shoulder" when left|right is not present. So only 3) return "shoulder"

re.compile(r'(?<!right|right\s*)shoulder')
sre_constants.error: look-behind requires fixed-width pattern

似乎我不能使用\ s *和"|"

It seems like I can't use \s* and "|"

我该如何解决.

提前谢谢！

推荐答案

regex模块:可变宽度后视

除了HamZa的答案之外，对于Python中任何复杂的正则表达式，我建议使用出色的 regex模块.它支持无限查找-这种功能的少数引擎之一，以及.NET和JGSoft.

regex module: variable-width lookbehind

In addition to the answer by HamZa, for any regex of any complexity in Python, I recommend using the outstanding regex module by Matthew Barnett. It supports infinite looknehind—one of the few engines to do so, along with .NET and JGSoft.

这使您可以执行以下操作:

This allows you to do for instance:

import regex
if regex.search("(?<!right |left )shoulder", "left shoulder"):
    print("It matches!")
else:
    print("Nah... No match.")

如果愿意，您也可以使用\s+.

You could also use \s+ if you wished.

输出:

It matches!

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