There is still a delta between how unicode behaves on 2 and how str behaves on 3, for example. In general, you'll be fine as long as you have a test suite that

There is still a delta between how unicode behaves on 2 and how str behaves on 3, for example. In general, you'll be fine as long as you have a test suite that runs in CI for both 2 and 3 - to catch incompatibilities early.