Configuring your git clone localy

Make sure that your .git/config has the following settings:

[remote "origin"]
    fetch = +refs/heads/*:refs/remotes/origin/*
    url = git+ssh://git@git.overlays.gentoo.org/proj/python.git
    pushurl = git@github.com:gentoo/python.git
    pushurl = git+ssh://git@git.overlays.gentoo.org/proj/python.git
[remote "github"]
    url = git@github.com:gentoo/python.git
    fetch = +refs/heads/*:refs/remotes/github/*

You can pull/push to both repos at once using --all switch.