Speaking as a maintainer of Mercurial and an avid user of Python, I feel like the experience of making Mercurial work with Python 3 is worth sharing because there are a number of lessons to be learned.

This post is logically divided into two sections: a mostly factual recount of Mercurial’s Python 3 porting effort and a more opinionated commentary of the transition to Python 3 and the Python language ecosystem as a whole. Those who don’t care about the mechanics of porting a large Python project to Python 3 may want to skip the next section or two

source: L