I think you&#x27;re exaggerating the obscurity of libraries that only run on python 2.<p>The list I&#x27;ve gone off of is <a href="https:&#x2F;&#x2F;python3wos.appspot.com&#x2F;" rel="nofollow">https:&#x2F;&#x2F;python3wos.appspot.com&#x2F;</a>. I use python a lot, and only now in late 2015 I might finally use python3 if starting a new project. When I started a new project last year, we used python2.<p>The biggest hold-out for me was gevent, which was only released 5 months ago. Gunicorn with gevent workers is my preferred stack for running python apps.<p>If you use protobufs or thrift, those both aren&#x27;t yet on python3.<p>The wall of shame currently lists requests as not working on python3, though I think that might be a fluke.<p>These ones might not be a deal-breaker since you can have a separate environment for infrastructure &amp; app code, but for some reason a lot of the infrastructure tools still haven&#x27;t updated to python 3 (supervisor, ansible, fabric, graphite).<p>All together, it adds up to a not-insignificant number of things that aren&#x27;t yet on python3. And even if nothing you use when you first start a project is python2 only, you have no idea what libraries you might need or want in the future and if those might be python2 only.