How to prevent "ImportError: No module named oauth2client.client" on Google App Engine?

I have this problem and solved by installing oauth2client with pip3:

pip3 install --upgrade oauth2client 

As per the google-api-python documentation, try this

pip install --upgrade google-api-python-client oauth2client

The answer is to "vendor" in the file(s).

We found a quick way to solve this based on this documentation https://cloud.google.com/appengine/docs/python/tools/libraries27#vendoring and this SO answer.

1. Create a new folder called "lib" in the same folder as your app.yaml file. (You can name it something else. Just use that name below.)

2. Create an empty file called appengine_config.py in the same folder as your app.yaml file

3. Add two lines to that appengine_config.py file:

   from google.appengine.ext import vendor vendor.add('lib')

4. From terminal, navigate to the directory which contains that file and execute the following command:

   sudo pip install -t lib google-api-python-client

The import error will disappear and you will have all the sub-dependent modules as well.