Add an opt-in timeout parameter to re to mitigate catastrophic backtracking

[tstefan (Stefan)]

@jb2170

with timeout(0.5):
    m = re.search(user_pattern, user_text)

The problem I see with such a generic solution is that it is quite brittle. The context manager with timeout could also be used to run any Python code. If the timeout fires, the cancellation (like triggered by a signal SIGALRM) could happen between any two bytecode instructions. So, if it was used in a generic way, it could leave any python object that is manipulated within the context manager in an invalid state (not keeping the invariants of the class). The Python docs explicitly warns about this problem. If it was restricted to the regex matching function, the semantics could be defined.

@Rosuav

For something completely generic like this, signal.alarm is probably the right choice. It wouldn’t be hard to make a context manager that sets an alarm and cancels it on exit.

That would not work under Windows, see docs.

@gcewing

This would still require cooperation from the C code doing the regex matching. Python signal handlers just set a flag and wait for the interpreter loop or something else to notice.

Correct, but this code exists and this is what allows you to abort your Python script also during Regex matches (like with Ctrl+C on Linux).

@Lucas_Malor

But such a proposal was already rejected. So I suppose your chances are low.

Not quite. Tim Peters asked for it to be discussed here first. This is what the OP did.