Most of this email thread is comparing Mercurial (Python) to Git. I'm not familiar enough with Git's internals to know why and where the languages are split, but it uses a significant amount of Shell scripting and Perl it its code base. You can put 'git-foo' anywhere on PATH and it'll get picked up. So in the comparison they're making startup time doesn't seem to be an issue for a combination of those languages, but it is for Python. It doesn't sound like their problem is that Python is an interpreted language.