Nick Coghlan: "One last fix needed to fully revert this is to remove the mention from the Python 3.5 What's New documentation: https://docs.python.org/3.5/whatsnew/3.5.html#os"

This sentence?

"The urandom() function now uses the getrandom() syscall on Linux 3.17 or newer, and getentropy() on OpenBSD 5.6 and newer, removing the need to use /dev/urandom and avoiding failures due to potential file descriptor exhaustion."

Why removing it? It's still correct that getrandom() is used by os.urandom() in the common case.

The corner case (urandom entropy pool not initialized) is already documented (including a "Changed in version 3.5.2: ..."):
https://docs.python.org/3.5/library/os.html#os.urandom

I don't think that it's worth to mention the corner case in What's New in Python 3.5.