Pub/Sub at GAE standard environment

Pub/Sub is also available in standard environments.However, the standard GAE environment does not include Cloud Pub/Sub Client Libraries as standard and should be included in the application code.For Python, the url below explains how to include it in the application code.
https://cloud.google.com/appengine/docs/standard/python/tools/using-libraries-python-27
Also, once the API library is included in the code, the usage is no different from that of a flexible environment.

In the standard environment, you can use Task Queue, which is very similar to Pub/Sub.If there is no problem, I think you can use Task Queue.Task Queue has documentation.

You can publish messages using the client library or the REST API.

If you want to subscribe to Pub/Sub messages on a GAE/SE, you can also receive messages by defining Push-type subscriptions and corresponding endpoints because you have never tried it, but I don't think the Pull type is available for GAE use.

See also

https://cloud.google.com/pubsub/docs/reference/libraries
https://cloud.google.com/pubsub/docs/push