frontend_utils.py

def api_url_for(endpoint, **values):
    # probably handle missing api_app key in some
    # special exception.
    api_app = current_app().config["api_app"]
    with api_app.app_context():
        return url_for(end_point, **values)
     

somefile.py

# Somewhere in an app factory


def make_app():
    #do some config tuff
    front_end_app.config["api_app"] = api_app

    app = DispatcherMiddleware(app, {
        '/frontend': front_end_app,
        '/api': api_app
    })
    return app