It was such a painful lesson, almost as painful as my previous bash lesson, only mildly less awful.
Le me once wanted to write pretty bash code:
~$ var=5 # Ugly!
~$ var = 5 # better...
… Only to realize that the second line is an error. The script I was modifying was not through interactive shell, so I had no idea what is was throwing errors… Till this day, whitespace haunts me in my sleep.
As for the regex part, it was this:
regex = r"(?:.*\n.*){0, 3}"
This looks like a perfectly healthy regex expression, except that it is not. Adding that extra space within the braces made the whole thing break and produced unpredictable results. Don’t do that.