sqlalchemy.util.langhelpers.safe_reraise

Reraise an exception after invoking some handler code. Stores the existing exception info before invoking so that it is maintained across a potential coroutine context switch. e.g.:: try: sess.commit() except: with safe_reraise(): sess.rollback() TODO: we should at some point evaluate current behaviors in this regard based on current greenlet, gevent/eventlet implementations in Python 3, and also see the degree to which our own asyncio (based on greenlet also) is impacted by this. .rollback() will cause IO / context switch to occur in all these scenarios; what happens to the exception context from an "except:" block if we don't explicitly store it? Original issue was #2703.