Continuing from the . The fact that Python interpreter didn't catch the regex pattern in tests but threw compile error on staging environment was very unsettling. Personally I knew that I am missing something on my part and I was very reluctant on blaming the language itself. Turns out, I was correct 🙈

I was looking for early feedback and comments on the post and Punch was totally miffed by this inconsistency and specially the conclusion I was coming to

Umm, I'm not sure I'm happy with the suggestion that I should check every regex I write, with an external website tool to make sure the regex itself is a valid one. "Python interpreter ka kaam main karoon abhi?" :frown:

He quickly compared the behavior between JS(compiler complianed) and Python(did nothing). Now that I had full attention from him there was no more revisiting this at some later stage. We started digging. He confirmed that the regex failed with Python2 but not with Python3.11 with a simple command

docker run -it python:3.11 python -c 'import re; p = r"\s*+"; re.compile(p); print("yo")'

I followed up on this and that was the mistake on my part. My local python setup was 3.11, I was using this to run my tests and staging environment was using 3.10. When I ran my tests within containerized setup, similar to what we used on staging, Python interpreter rightly caught faulty regex:

re.error: multiple repeat at position 11

Something changed between python 3.11 and 3.10 release. I looked at the release logs and noticed this new feature atomic grouping and possessive quantifier. I am not sure how to use it or what it does 1. But with this feature, python 3.11 regex pattern: r"\s*+" is a valid one. I was using this to run tests locally. On staging we had python 3.10, and with it interpreter threw an error.

Lesson learned:

I was testing things by running things locally. Don't do that. Setup a stack and get is as close to the staging and production as possible. And always, always run tests within it.

You pull an end of a mingled yarn,

to sort it out,

looking for a resolution but there is none,

it is just layers and layers.