gistfile1.py

def launchUpdate(updated, user, ticket, appdata=None):
    if appdata:
        appdata = os.path.abspath(appdata)

        if sys.platform == "win32":
            os.putenv("APPDATA", appdata)
        else:
            os.environ["HOME"] = appdata

    url = "minecraft.jar?user={0}&ticket={1}".format(user, ticket)
    line = r'java -cp "{0}/.minecraft/bin/minecraft_launcher.jar" ' + \
        r'-Djava.library.path="{0}/.minecraft/bin/natives" ' + \
        r'net.minecraft.GameUpdater "{1}" "{2}"'
    
    line = line.format(appdata, updated, url)
    
    mc = subprocess.Popen(line, env=os.environ)
    mc.wait()

the function is sent data from the login, as well as the directory where you want stuff stored (portability)