About ""No parents, no children", that's fine so far as it goes.  But Python isn't C, a threading.Thread is not a POSIX thread, and threading.py _does_ have a concept of "the main thread".  There's no conceptual problem _in Python_ with saying "the main thread" waits to .join() other non-daemon threading.Threads at process exit.  No parent/child relationships are implied by that either - it's just the concept that one thread is distinguished.