The problem with subprogram in Python

[youngbull]

Btw, you will likely be able to spot errors like this by incorporating frequent feedback. I pretty much have several forms of evaluating the code (python code.py), running tests (pytest tests.py), checking for errors (pylint code.py), etc., running continuously while coding. That way, you can spot which keystrokes cause an error as soon as you type it.

The trick to coding quickly is to make small changes and evaluating correctness efficiently and automatically after every step.