Until you need to use some library that doesn't support python3. I think I've made the transition from python3 to python2 more than I have the other way around.
Is there some sort of failure mode you're thinking of where I'd still see all the tests run but the test framework would give false success for something?
More and more of the bigger libraries are ported already, and a lot of the others have been replaced by newer libraries that work with Python 3. If the library you're trying to use doesn't support Python 3, it's probably a good indication most people have moved on to something better...
>>> b"%u" % 5
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: unsupported operand type(s) for %: 'bytes' and 'int'If I remember right, % used to be deprecated in Python 3, but was undeprecated again by popular demand.
json.loads(foo) blahblahException foo is bytes not text.
That said I still endorse py3 for new things