Bug report

Bug description:

finalizer=lambda*a:Nonetry:sys.set_asyncgen_hooks(firstiter="invalid",finalizer=finalizer)exceptTypeError:# TypeError due to invalid `firstiter` typecur=sys.get_asyncgen_hooks()self.assertIsNone(cur.firstiter)# This is not setself.assertIsNone(cur.finalizer)# But this is set

PEP 525 doesn't imply or define partial initialization priority. Since inside ofset_asyncgen_hooks is blackbox to user, this is surprising and users are hard to know they have to back up current setup and recover it whenTypeError happens.

Inconsistency also cause user experience problem. Current ordersys.set_asyncgen_hooks(firstiter="invalid", finalizer=finalizer) causes partial set, butsys.set_asyncgen_hooks(firstiter=finalizer, finalizer="invalid") will not.

CPython versions tested on:

CPython main branch

Operating systems tested on:

macOS

Linked PRs

• gh-118473: Fix set_asyncgen_hooks not to be partially set when arguments are invalid #118474