[nedbat]

Yes, but why do I need to know that as a Python programmer? What mistakes might I make if I don't know about it?

[vacuity]

I was just making it clear that the OS policy pervades. That is, the developers of CPython or another execution context need to care about it, and so it informs some of the implementation details that may leak into programs. We agree that Python presents an abstraction so that Python programmers (usually) don't have to see this.