NameError: name 'oauth2' is not defined when running client library setup code

When running the code in https://github.com/googleads/googleads-python-lib/wiki/API-access-on-behalf-of-your-clients-(web-flow)#step-2---setting-up-the-client-library I am encountering NameError: name 'oauth2' is not defined. This seems to be correct because there is no import anywhere of any oauth2 namespace.

If I change the code to

from google import oauth2
import google.oauth2.credentials
import google_auth_oauthlib.flow

flow = google_auth_oauthlib.flow.Flow.from_client_secrets_file(
    'client_secrets.json',
    scope=[oauth2.GetAPIScope('adwords')])

I get a new error: AttributeError: 'module' object has no attribute 'GetAPIScope'

Review Step 2 of the linked wiki page, especially the oauth2 reference and the google_auth_oauthlib.flow.Flow.from_client_secrets_file example. Verify the documented imports and scope helper against the current Python client setup, then update the example so it runs without the reported NameError or AttributeError.