I find it a lot easier to appreciate patches that implement a single change than those that mix different changes. There are three different things in your patch, which I would like to see in at least three different commits. I'd be happy if you could separate the changes into more readable feature patches. That makes it easier to accept them.

I'm generally happy about the slice changes, but you will have to benchmark the equivalent changes in Py3.2 to prove that they are similarly worth applying there.