Comment 2 for bug 1217194

https://pypi.python.org/pypi/re2/

Is a python wrapper around google's re2 regex package. It provides the same functionality as most of perl's syntax, although it drops support for backrefs altogether. There's no way to really detect catastrophic backtracking 100% of the time (sans manual intervention), so I think it makes sense to drop the support for backrefs altogether.