https://docs.python.org/3/tutorial/index.html
I found it really helpful.
From Py1.52 I've done the same.
I wish every language was as well documented (Perl6 is pretty good) [0] as Py, especially the changes b/w versions. Rough order of reading: What's new, Tutorial, PEPs, Library references. Why is it good? It is canonical, pushed out as a release is done, comes with the install (cf: $ pydoc foo) and is free.
Python is also rather outstanding in the sense that there are tons of good recordings of PyCon talks that explain almost every language feature in very approachable ways.
The quality of those talks is usually great too, it seems that PyCon consistently hosts very good speakers.
I'm only starting to realize, as I branch in to other things, that this might not be the norm.
This( + no longer allowing "encoding" of bytes or "decoding" of unicode) means that you have a much higher chance of writing correct code when it comes to handling encodings.
As someone who writes a _lot_ of Python code (mostly in 3 but with occasional switches to 2), who maintains several libraries which work in both 2 and 3, and as someone who uses a wide range of libraries in stats, machine learning, networking, web development, etc. in my python 3 work...this piece seems totally disconnected from reality. The problems it describes are relentlessly overblown when they're not simply manufactured from whole cloth.
Put another way: the differences between 2 and 3 are not great, the vast majority of libraries you'd want to use (i.e. are actively maintained or of at least good quality) work in 3, and while I don't doubt there's great piles of Python 2 code moldering away big "enterprise" apps and those sorts of places, it's ever been thus in that space, no matter what the language, and doesn't pose any sort of existential threat to Python.
(edit: I used to recommend "Learn Python The Hard Way" to newcomers, and have just kept reflexively doing that over the years because I wasn't aware of a better resource. But if this article has accomplished one thing, it's that it's spurred me to look for a replacement)