Empty matches in Python’s `re` module

https://blog.narf.ssji.net/2025/04/30/empty-matches-in-pythons-re-module/

Python’s `re.sub` method has a weird, though documented, behaviour.

Replacements for empty-matching patterns such as `/.*/` applied to a non-empty string will lead to two matches. The replacement will therefore be applied twice.

A simple fix is to make sure the pattern is not empty-matching, e.g. `/.+/`.

#debugging #Python #regexps #sed

Best answer on regexps ever? 🧐 😎

- What is the plural form of regex?

- If you've used more than one of them, you'll know that the plural of "regex" is "regrets." – cjs (Mar 14, 2022 at 23:46)

#regex #regexps #programmer #programming #devops #regularexpression

Extended #regexps are great for place names like "Wellesley" where you can not remember if it's Welesley, Welleseley, Wellesselley, Welleslley, or Welesslley to save your dadburn life. ;)

/wel+es+e?l+ey/ !!!

cc: @amin

I had a problem. I used #regexps... and I tested them. Througly. I cut them down in pieces. And tested the pieces first...

And now I don't have a problem!

Test! And don't forget to also test your regexps!

#til

* Base64 is not idempotent:`b64(x)` != `b64(b64(x))`. This is because it represents values 0-63 with values 65-90 (`A-Z`), 97-122 (`a-z`), 48-57 (`0-9`), 43 (`+`) and 47 (`/`); and 61 (`=`) for padding.
* `grep` not only has options to support more complex #regexps (`-E, --extended-regexp`, `-P, --perl-regexp`), it also has `-F,--fixed-strings` to treat the pattern as just a string. This not only makes it slightly faster, it's easier to write if you would need too much escaping.

Any #RakuLang core hackers want to take up this challenge?

#RegularExpressions #RegExps #RegExes #RegEx https://ruby.social/@gd/110718818730295923