As we already mentioned, our REST API will be integrated with the existing App Engine application without altering its behavior, so we need to specify a new WSGI application that will handle the URLs we map to the API endpoints. Let's start with the app.yaml file, where we add the following code:

handlers:
- url: /static
  static_dir: static

- url: /_ah/spi/.*
  script: notes_api.app

- url: .*
  script: main.app

libraries:
- name: webapp2
  version: "2.5.2"

- name: jinja2
  version: latest

- name: endpoints
  version: 1.0

The regular expression that matches API URLs is actually /_ah/spi/.*. Even if we perform requests to an URL such as https://example.com/_ah/api/v1/an-endpoint, Cloud Endpoints will take care of the proper redirects. The handler script of the API URLs points to the app variable in the notes_api module, which we are yet to create. In a new file called notes_api.py, we add the following code:

import endpoints

app = endpoints.api_server([])

This...