This script clones a repository from Github, previously forked, and add both remotes origin and upstream, renaming origin with your username.

git-clone.py

#!/usr/bin/python

import sys
from os.path import splitext, basename
from os import system
import re

# Verify arguments
try:
    urlForked = sys.argv[1]
    urlUpstream = sys.argv[2]
except Exception:
    print "Usage: git-clone <origin> <upstream>"
    sys.exit(1)

repoName = splitext(basename(urlUpstream))[0]
userName = re.search(r'\D*github.com[/:]([^/?]+)', urlForked).group(1)

bashCommand = '''
git clone {0} {1}
(
    cd {1}
    git remote rename origin {2}
    git remote add upstream {3}
)
'''.format(urlForked, repoName, userName, urlUpstream)

system(bashCommand)