At least in my experience, they are pretty similar. Most of my Python 2 knowledge works fine in Python 3. I think it's really a stretch to pretend like your knowledge from 2 would be that divergent. I'm sure "in some senses" your statement is correct, but in practice I've seen few major changes. Learning Python 2 is the same as learning Python 3 and vice-versa; there are a few significant caveats between them, but I have never felt that they were "practically two different languages".