Comment by jordigh

Behold the tremendous amount of effort for Mercurial:

https://www.mercurial-scm.org/repo/hg/log?rev=py3&revcount=2...

They've been porting hg into Python 3 for the last 10 years and are only now nearing completion.

I've written a bit more about this in Lobsters:

https://lobste.rs/s/3vkmm8/why_i_can_t_remove_python_2_from_...