Today I wrote a new blog post at ticketea's engineering blog. Update: Blog no longer accessible but you can download the article in PDF from here: how we migrated ticketea.com to Python 3 in two weeks.
It was an interesting task, and I think went well because "ignorance is bliss", as I hadn't used Python 2 I wasn't biased by fear nor knew the real reach of possible failures, so I just went on, fixing every single error and testing and testing and testing again until all looked fine, and then more tests.
Some libraries already had Python 3 branches (outdated but with quite some work done) and QA helped me so the merit is not mine alone, but I'm quite happy with the result and it is a pleasure to focus on just Python 3.6 (plus now we can start adding type hinting and other fancy stuff).
Fun fact: All of this originated with the desire to add rate limiting to a new (internal) API I was building. I will actually write here a small blog post about rate limits because I found two very good links with nice explanations and I think can be of use for others in search of similar features.