gh-130273: Fix traceback color output with unicode characters by grayjk · Pull Request #142529 · python/cpython

Thanks for your PR.

I reverted the move of string-handling utils to traceback, they don't belong there
Now those utils are copied into traceback temporarily so that we can backport the fixes to older bugfix branches (3.13 and 3.14). In main I will do a follow-up change where those utils are moved to string/__init__.py where they belong.

This is because mypy type-checking introduction to the standard library relies on introduction of fully type-annotated libraries. I intend to keep it that way and therefore sprinkling type: ignore is not a solution.

It is now out of scope to format all of traceback.py for 3.15 while string.py is just three small classes and a function (two more functions if we count string.templatelib). When I make this change, I will also undo the unicodedata conditional import shenanigans and use lazy imports. That's also why this will be a main-only change.

There's also a related behavioral change in _display_width that I feel is part of this fix. It introduces handling of pre-existing terminal escape sequences in the exception strings (as well as any stranded ^Z characters but those are admittedly unlikely to be part of tracebacks).