On Fri, May 1, 2020 at 10:58 PM Andrew Barnert via Python-ideas <python-ideas@python.org> wrote:
A separate function can be used in third-party libraries immediately, as long as there’s an available backport (whether that’s more-iterools, or a trivial zip39 or whatever) that they can require; a flag can’t be used in libraries until they’re able to require Python 3.9 (unless they want to use a backport that monkey patches or shadows the builtin, but I doubt you’d suggest that, since you called it an antipattern elsewhere in the PEP).

Specifically the PEP says:

Another proposed idiom, per-module shadowing of the built-in zip with some subtly different variant from itertools, is an anti-pattern that shouldn't be encouraged.

I think the PEP is saying it'd be an antipattern to shadow zip with a version that is always strict. If you want both strict and non-strict in the same file, you're in trouble. But replacing zip with a zip that has an optional strict flag should be harmless. So a backport with a flag seems perfectly fine, whether it's used per module or it patches builtins for all modules.