Parts of Twisted. But open source projects are not the problem. We (a major scientific collaboration) have likely millions of lines of Python (2). Mostly used i

Parts of Twisted. But open source projects are not the problem. We (a major scientific collaboration) have likely millions of lines of Python (2). Mostly used in one-off plotting scripts, or as configuration or steering files. On the one hand, I bet >95% of these scripts translate perfectly with 2to3.py, have no unicode/str confusion issues, and would be trivial to port. It's often really just the "print". On the other hand, most of this is "legacy" code, and there is no benefit to port it - we'd rather not mess with code that is supposed to be "frozen" and e.g. able to reproduce past scientific results, and nobody will spend time porting it without tangible benefits. Last I checked, it was considered "too hard" to move to Python3, but in the meantime we are switching VCS (from SVN(!) to git), we are rewriting our main framework to be multithread-capable, and tackling a bunch of other gargantuan tasks. So if going to Python3 is harder than all that, then I think something went wrong with the transition. (For the record, for personal projects I use Python3 now, as everything has catched up for me.)