According to the man page, find -print0 and xargs -r are also GNU extensions. Even though they work on OpenBSD (do they?), they could still break on some platforms.

As find -exec cmd {} ';' is already used for everything but __pycache__, I'd rather only change the removal of __pycache__. I believe there are more files that match '*.py[co]' than '__pycache__', and people are already waiting for a separate rm process to be invoked on each *.py[co], so invoking a separate rmdir for each __pycache__ shouldn't make it much slower.