You may be thinking of Python's "significant whitespace". But all that does is indicate nested blocks.

This works exactly the same in a proportional or monospaced font. The only thing Python cares about is how many spaces or tabs you have at the beginning of a line, and that you don't mix the two.

There are coding styles that don't look as good in a proportional font, such as this kind of "column alignment" or "hanging indent":

  def function_with_a_long_name(first_param_with_a_long_name,
                                second_param_with_a_long_name,
                                third_param_with_a_long_name):
      pass

The most popular Python code formatter, Black, only uses indentation and no column alignment. Here is how it formats that code:

  def function_with_a_long_name(
      first_param_with_a_long_name,
      second_param_with_a_long_name,
      third_param_with_a_long_name,
  ):
      pass

https://black.readthedocs.io/en/stable/

If I had to pick one to use with a proportional font, I guess it would be Perl. The aesthetics would at least fit it well.

It works because the spaces are nice and wide unlike in a typical proportional font.

I don’t use it anymore mostly because I wanted something with a little more character but it’s worth a try.

[1]: https://djr.com/input/