def load_packages(env, reinstall=False):
    config = env.load_config()
    package_root = env.project.get_package_cache_path()
    update_cache(package_root, config['PACKAGES'],
                 os.path.join(env.root_path, 'packages'),
                 refresh=reinstall)
    add_site(package_root)
This loads all the packages of a project.  What this does is updating
dataset/ETHPy150Open lektor/lektor/lektor/packages.py/load_packages