The RE engine here is only used as a fast VM; so the pathological cases from the article should still apply. So apart from the memory use issues there's also that.

It should be updated with a functools.lru_cache decorator I think.

That's an old version of Python source from a mirror. It uses functools.lru_cache with a maxsize of 256 now: https://github.com/python/cpython/blob/fcfe80ec2592fed8b3941...