I presume the issue here is that Hg is so complicated that everyone knows a different subset of the commands and semantics.I personally don't know what the commands for cherry-picking a revision would be.
I also don't know exactly what happens when you merge a PR using bitbucket. (I'm only familiar with the GitHub PR flow, and I don't like its behavior, which seems to always create an extra merge revision for what I consider as logically a single commit.)
BTW When I go to https://bitbucket.org/larry/cpython350 the first thing I see (in a very big bold font) is "This is Python version 3.6.0 alpha 1". What's going on here? It doesn't inspire confidence.