It would be nice to document the bpo-40222 changes in What's New in Python 3.11 and in the CodeType documentation: * https://docs.python.org/dev/library/types.html#types.CodeType * https://docs.python.org/dev/whatsnew/3.11.html Users of types.CodeType.replace(co_code=new_code) must now pass co_exceptiontable or exception handling will no longer work as expected. Callers are responsible to build co_exceptiontable. Currently, the format of this table is documented at: https://github.com/python/cpython/blob/main/Objects/exception_handling_notes.txt There is no public function to encode this table, it's also the responsibility of the caller. See also bpo-47185 "code.replace(co_code=new_code) no longer catch exceptions on Python 3.11" closed as "won't fix" for the background.