python正则表达式来检测一个词是否存在 [英] python regex to detect a word exists

问题描述

我想使用 python 正则表达式检测一个词是否在一个句子中.另外，希望能够否定它.

I want to detect whether a word is in a sentence using python regex. Also, want to be able to negate it.

import re
re.match(r'(?=.*\bfoo\b)', 'bar red foo here')

这段代码有效，但我不明白为什么我需要把 .* 放在那里.还要否定它，我不知道该怎么做.我试过了:

this code works but I do not understand why I need to put .* in there. Also to negate it, I do not know how to do that. I've tried:

re.match(r'(?!=.*\bfoo\b)', 'bar red foo here')

但它不起作用.我的最终目标是像这样组合它们:

but it does not work. My ultimate goal is to combine them like so:

re.match(r'(?=.*\bfoo\b)(?!=.*\bbar\b)', 'bar red foo here')

推荐答案

要检测字符串中是否存在某个单词，您需要正向前瞻:

To detect if a word exists in a string you need a positive lookahead:

(?=.*\bfoo\b)

.* 是必要的，以便能够在字符串开头之外进行更远的搜索(re.match 将搜索锚定在字符串开头).

The .* is necessary to enable searching farther than just at the string start (re.match anchors the search at the string start).

要检查字符串中是否没有单词，请使用否定前瞻:

To check if a string has no word in it, use a negative lookahead:

(?!.*\bbar\b)
 ^^^

所以，将它们结合起来:

So, combining them:

re.match(r'(?=.*\bfoo\b)(?!.*\bbar\b)', input)

将在包含整个单词 foo 且不包含整个单词 bar 的字符串中找到匹配项.

will find a match in a string that contains a whole word foo and does not contain a whole word bar.

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