How to speed up regex findall in a CSS file

Question

I'm using regex to find all selectors in CSS files and sometimes, it loads for minutes. After looking at the files, I found out that the sourceMappingURL is really large and cause the issue:

sourceMappingURL=data:application/json;charset=utf8;base64,eyJ2ZXJzaW9uIjozLCJzb3VyY2VzIjpbIndvb2QuZnVsbC5taW4uY3NzIl0sIm5hbWVzIjpbXSwibWFwcGluZ3MiOiJpQkFFQSw4QkFBOEIsU0FBUyxPQUFPLGlCQUFpQixPQUFPLEtBQUssb0JBQW9CLEtBQUssUUFBUSxPQUFPLEVBQUUsU0FBUyxtQkFBbUIsSUFBSSxRQUFRLFdBQVcsT0FBTyxvQkFBb0IsNEJBQTRCLE9BTyxL...

Here's the full CSS file: https://jsfiddle.net/jj_jaq/32d7hpc0/3/

Here's my regex:

selectors = re.findall(r'([.#\w][-\w,\s.]+)(\{(.*?)\})', content)

Is there a way to speed up my regex?

See [Can I improve performance of this regular expression further](https://stackoverflow.com/questions/33869557/can-i-improve-performance-of-this-regular-expression-further/33869801) — Wiktor Stribiżew, Feb 05 '20 at 09:35
Please post the real string you have trouble with. A link to pastebin.com will do. — Wiktor Stribiżew, Feb 05 '20 at 09:49
I think I have found a hack, try `[.#]?\b([-\w,\s.]+){([^{}]*)}`, see [demo](https://regex101.com/r/Knm2VE/2). Still a bit slow, but seems working. — Wiktor Stribiżew, Feb 05 '20 at 10:16
waow, it seems to work ! Thanks @WiktorStribiżew. Do you know what exactly was slowing the process down? — jjyoh, Feb 05 '20 at 10:29

score 1 · Accepted Answer · answered Feb 05 '20 at 10:32

You may tell the regex engine to anchor the matches at left-hand word boundaries. However, just adding \b won't work as the first char you want to match can also be a . or # that are non-word chars.

Use

[.#]?\b([-\w,\s.]+){([^{}]*)}

See the regex demo where [.#]? matches an optional . or # before the word boundary check.

How to speed up regex findall in a CSS file

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