Bug report

Bug description:

Repro: Check out this commit, build, and run python -mtest test_monitoring -mtest_implicit_stop_iteration.

Context: The unspecialized implementation of FOR_ITER has some built-in opcode fusion, in that it skips the following END_FOR and POP_TOP when tp_iternext returns NULL. When the iterator is a generator, as it is in ExceptionMonitoringTest.test_implicit_stop_iteration(), that means we skip the monitor_stop_iteration() call in INSTRUMENTED_END_FOR.

test_implicit_stop_iteration() passes as written, though, because the FOR_ITER in the helper function has been specialized to FOR_ITER_GEN by the time the generator finishes, and FOR_ITER_GEN's implementation doesn't perform the same fusion as FOR_ITER.

This bug can be exposed by making this change to test_implicit_stop_iteration(), so the FOR_ITER stays unspecialized while iterating over the generator in question.

CPython versions tested on:

CPython main branch

Operating systems tested on:

Linux

Linked PRs

• GH-116090: Fix test and clarify behavior for exception events when exhausting a generator. #120697
• GH-116090: Fire RAISE events from _FOR_ITER_TIER_TWO #122413
• [3.13] GH-116090: Fire RAISE events from _FOR_ITER_TIER_TWO (GH-122413) #122419