I am using my proportional font in Python too. The meaningful spaces are at the beginning of the line. 4 monospaced spaces become 4 narrower spaces, 8 monospaced spaces become 8 narrower spaces and they are still twice as wide as the 4 spaces.

I never had problems with Ruby, Python, JS, Elixir, Perl and probably other languages I used a little in the last 15 years or more. HTML and CSS too.