Python2 is getting much harder to install so it would be nice if this repo was updated to work with python 3. I just inspected the fetch-externals script and I think it can be fixed by changing line 32 to be exec(f.read(), globals()) and that seems to make it work with python3 (at least it doesn't seem to be failing with any errors).

I can make a PR of this if there is someone to review it.

Edit: I made the PR as I needed to put it in a fork anyway.