如何删除两个特定的chaster

Question

I have the following text:

rule="Aa&~a->c"

and I need to remove the letter a that is alone with the ~ sign so far I tried this regex expression:

auxRegla=re.sub(r"(?<!~)\ba\b",r"",regla)

the \\ba\\b are to set the boundaries and that works just fine and the (?<!~) has the intention to remove the ~ sign, but those two togethere aren't doing anything.

I need the result to be:

Aa&->c

Answer 1

You should not use a negative lookbehind here, since you do want to match ~ . You can match ~a directly instead, but with a word boundary assertion after a :

re.sub(r"~a\b", '', regla)

Answer 2

First of all, you are using lookbehind for ~ , which will match the thing inside, but will not consume it (to put it simply it will not remove the ~ , only a 's that are prepended with it).

Second, you are using the negative lookbehind, so your regex matches a 's NOT prepended with ~ .

Better regex for you is ~a\\b (no first word boundary \\b since ~ is definitely not a word character, and a definitely is, so it is always true)