Bug report

Python 3.12.0a7 (at least as of commit d65ed69) can fail to catch exceptions when an iterator is involved. The following code works on Python 3.11 but the ValueError is uncaught on Python 3.12:

#!/usr/bin/env python

def do_work():
    yield
    raise ValueError()


def main():
    try:
        for _ in do_work():
            if True is False:
                return
    except ValueError:
        pass


if __name__ == '__main__':
    main()

With this code in repro.py the following traceback is shown on Python 3.12:

Traceback (most recent call last):
  File "//repro.py", line 18, in <module>
    main()
  File "//repro.py", line 12, in main
    return
  File "//repro.py", line 5, in do_work
    raise ValueError()
ValueError

No error or output occurs under Python 3.11.

Your environment

Tested on Ubuntu 20.04.5 using the deadsnakes nightly build: python3.12 - 3.12.0~a7-98-gd65ed693a8-1+focal1

Linked PRs

• GH-103488: Use return-offset, not yield-offset. #103502