正则表达式匹配除给定正则表达式之外的所有内容 [英] Regular expression matching everything except a given regular expression

问题描述

我试图找出一个正则表达式来匹配任何不以 mpeg 开头的字符串.对此的概括是匹配任何不以给定正则表达式开头的字符串.

I am trying to figure out a regular expression which matches any string that doesn't start with mpeg. A generalization of this is matching any string which doesn't start with a given regular expression.

我尝试了如下:

[^m][^p][^e][^g].* 

问题在于它要求字符串中至少有 4 个字符.我无法找到一种很好的方法来处理这个问题，也找不到一种通用的方法来处理这个问题.

The problem with this is that it requires at least 4 characters to be present in the string. I was not able to figure out a good way to handle this and a generalized way to handle this in a general purpose manner.

我将在 Python 中使用它.

I will be using this in Python.

推荐答案

^(?!mpeg).*

这使用负前瞻来仅匹配开头不匹配 mpeg 的字符串.本质上，它要求字符串开头的位置不能是一个位置，如果我们开始匹配正则表达式 mpeg，我们可以成功匹配"——从而匹配任何不以 mpeg 开头的内容，并且不匹配任何匹配的内容.

This uses a negative lookahead to only match a string where the beginning doesn't match mpeg. Essentially, it requires that "the position at the beginning of the string cannot be a position where if we started matching the regex mpeg, we could successfully match" - thus matching anything which doesn't start with mpeg, and not matching anything that does.

但是，我很好奇您使用它的上下文 - 除了正则表达式之外，可能还有其他选项会更有效或更易读，例如...

However, I'd be curious about the context in which you're using this - there might be other options aside from regex which would be either more efficient or more readable, such as...

if not inputstring.startswith("mpeg"):

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