用于检测未用双引号括起来的字符串的正则表达式 [英] A regex to detect string not enclosed in double quotes

问题描述

我有一个类似这样的字符串

quick"brown"狐狸over"the"懒狗

我需要一个正则表达式来检测没有用双引号括起来的单词.经过一些随机尝试后，我发现了这个 ("([^"]+)").这检测到一个用双引号括起来的字符串.但我想要相反的.我真的想不出来即使在尝试反转上述正则表达式之后.我在正则表达式方面很弱.请帮助我

解决方案

使用前瞻/后视断言:

(?

示例:

<预><代码>>>>进口重新>>>a='"quick" "brown" 狐狸跳过 "over" "the"lazy dog'>>>print re.findall('(?

这里的主要内容是前瞻/后视断言.您可以说:我希望在表达式之前使用这个符号，但我不希望它成为匹配本身的一部分.好的.为此，您使用断言:

(?

这是一个消极的回顾.这意味着您想要 abc 但没有 [\S"] before，这意味着必须没有非空格字符(开头的word) 或 " 之前.

这是相同的，但方向相反:

abc(?![\S"])

这是一个负面的前瞻.这意味着你想要 abc 但没有 [\S"] after 它.

该类型一般有四种不同的断言:

(?=pattern)是一个积极的前瞻断言(?！图案)是一个否定的前瞻断言(?<=模式)是一个积极的回顾断言(?<! 模式)是一个否定的回顾断言

I have a string something like this

"quick" "brown" fox jumps "over" "the" lazy dog

I need a regex to detect words not enclosed in double quotes. After some random tries I found this ("([^"]+)"). This detects a string enclosed in double quotes. But I want the opposite. I really can't come up with it even after trying to reverse the above mentioned regex. I am quite weak in regex. Please help me

解决方案

Use lookahead/lookbehind assertions:

(?<![\S"])([^"\s]+)(?![\S"])

Example:

>>> import re
>>> a='"quick" "brown" fox jumps "over" "the" lazy dog'
>>> print re.findall('(?<![\S"])([^"\s]+)(?![\S"])',a)
['fox', 'jumps', 'lazy', 'dog']

The main thing here is lookahead/lookbehind assertions. You can say: I want this symbol before the expression but I don't want it to be a part of the match itself. Ok. For that you use assertions:

(?<![\S"])abc

That is a negative lookbehind. That means you want abc but without [\S"] before it, that means there must be no non-space character (beginning of the word) or " before.

That is the same but in the other direction:

abc(?![\S"])

That is a negative lookahead. That means you want abc but without [\S"] after it.

There are four differenet assertions of the type in general:

(?=pattern)
    is a positive look-ahead assertion
(?!pattern)
    is a negative look-ahead assertion
(?<=pattern)
    is a positive look-behind assertion
(?<!pattern)
    is a negative look-behind assertion 

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