If you want to use 3rd party libraries that are not included this list, then you'll have to add them manually.
In order to include manually any other library you have to have them inside the directory where the app.yaml lives. So for example if you have the following structure:
hello
├── libs
│ └── bs4
├── hello.py
└── app.yaml
then in your hello.py you have to put these two lines in the beginning of the file:
import sys
sys.path.insert(0, 'libs')
After doing that you'll be able to use any 3rd party library that you're going to put in that libs directory. For example:
from bs4 import BeautifulSoup
Update
Since you're using that framework, rollback your changes and use the same pattern as they are using for flask or werkzeug or other 3rd party libraries. Just put the bs4 in the src directory and try to include it normally.
