Eliminate Python __pycache__ directories

Python ≥ 3.8 can put all Python .pyc cache files under one system-wide directory by the PYTHONPYCACHEPREFIX environment variable. For Windows, set environment variable PYTHONPYCACHEPREFIX to %temp%. For MacOS / Linux in .bashrc, .zshrc or other appropriate shell configuration file add the line export PYTHONPYCACHEPREFIX=$TMPDIR

Python < 3.8 can also avoid writing .pyc files anywhere with the PYTHONDONTWRITEBYTECODE environment variable. For Windows, set environment variable PYTHONDONTWRITEBYTECODE to 1. For MacOS / Linux in .bashrc, .zshrc or other appropriate shell configuration file add the line export PYTHONDONTWRITEBYTECODE=1.