[nas]

The unicode/bytes change it the most time consuming in my experience. Second comes the fact that you can't sort arbitrary types anymore and that None is no longer smaller than any other value.

In order to ease porting, I've created a modified Python 3.6 interpreter that generates warnings in a lot of the cases that real Python 3 would generate an exception. See https://github.com/nascheme/ppython .

The goal is to have a 2to3 script that generates something that will run, with warnings, under me modified Python. Once you fix all the warnings, your code should run correctly in Python 3.

[orf]

> Second comes the fact that you can't sort arbitrary types anymore

Surely that's a bug in the system that you've just uncovered and fixed? Py2 used to use the memory address of the object when comparing by default, which is just... crazy, especially for a language with so few WTFs:

   >>> object() > object()
   True
   >>> object() > object()
   False
   >>> object() > object()
   True
   >>> object() > object()
   False

> In order to ease porting, I've created a modified Python 3.6 interpreter

That looks amazing! We're going to end up porting a fairly large + critical Django app to py3 and I definitely think this could ease some of the pain. I'm going to give it a go when I get the chance.

[dragonwriter]

> Py2 used to use the memory address of the object when comparing by default, which is just... crazy,

Its true that that's crazy, but, OTOH, everything-can-be-sorted is a useful feature (which Erlang has, for instance). Py3 could conceptually have retained it with a different implementation (this would probably still have been a breaking change from Py2, but not a feature loss.)