For gits looking to transition to hg (namely to work on cpython): http://demianbrecht.github.io/vcs/2014/07/31/from-git-to-hg/.
My learnings beginning to work with mercurial while working on the stdlib. (This was sent out to core-mentorship already, just figured this is likely a larger audience with potentially more interested people making the same transition) -- Demian Brecht http://demianbrecht.github.com -- https://mail.python.org/mailman/listinfo/python-list
