Wow, didn't expect this to make the front page of HN. There's more context in the groups thread (http://groups.google.com/group/python-tornado/browse_thread/...), but the short version is that a change to abstract away some error handling with the python 'with' statement had a surprising performance impact. When used with the @contextlib.contextmanager decorator, the with statement is more than 25 times as expensive as a try/except statement.