I think (a) is true, yes. I've written about the migration of KDE from SVN to Git in a longer comment elsewhere in this thread, and Qt (not a language, but the

I think (a) is true, yes. I've written about the migration of KDE from SVN to Git in a longer comment elsewhere in this thread, and Qt (not a language, but the library framework most of KDE's products build upon) switching to Git was definitely a significant factor in Git gaining traction among members of the KDE community. The KDE community consciously wanted to harness the potential synergy it saw in the KDE and Qt ecospheres syncing up on the same VCS. OTOH, I think the Python community is pragmatic enough that it wouldn't have chosen Mercurial over Git if it being written in Python would have been the only point in Mercurial's favor, from the POV of their requirement set. But it probably does have an emotional/affinity effect, after all language developers do obviously have to care about language! :) Interestingly, one of the best Git libraries around is actually a pure Python implementation of Git and its protocols: Dulwich.