In which file did you encounter the issue?

/appengine/standard/flask/hello_world/main.py

Did you change the file? If so, how?

no

Describe the issue

Like it is said in the guide, "Flask is bundled into the runtime". I suppose as long as flask is added to libraries in app.yaml, I should be able to import it from main.py. That is what has been implemented after this commit. But I still get ImportError: No module named flask.

I've tested on online console and local env that I can't import flask simply by adding it to app.yaml, and I tested PIL in the same way, which managed to be imported.