Python Regular Expression - Match pattern that does not contain a string

Question

I'm quite new to regular expression, and have been searching around for away to do this without success. Given a string, I want to remove any pattern that starts with "abc", ends with "abc", and does not contain "abc" in the middle. If I do

'abc.*(abc).*abc'

it will match any patter starts with "abc", ends with "abc", and does contain "abc" in the middle. How do I do the opposite. I try

'abc.*^(abc).*abc'

but it won't work.

Answer 1

You can try the following pattern :

^abc((?!abc).)*abc$

(?!abc) is Negative Lookahead - Assert that it is impossible to match the abc inside your string.

Debuggex Demo

Answer 2

Your syntax for trying to negate part of your pattern is incorrect.

Also, ^ outside of a character class asserts position at the beginning of the string. You need to use a Negative Lookahead assertion and be sure to anchor the entire pattern.

^abc(?:(?!abc).)*abc$

Live Demo