> If you are upgrading or downgrading the python interpreter, then you probably should also delete all __pycache__ folders, these folders hold the binary files

> If you are upgrading or downgrading the python interpreter, then you probably should also delete all __pycache__ folders, these folders hold the binary files that hold the compiled bytecode instructions, but you can't be sure that these will work after a version change! This is incorrect. Python bytecode files are versioned alongside the interpreter, so when CPython finds a __pycache__/*.pyc file which is the wrong version, it will just ignore it and won't cause any problems.