ModuleNotFoundError: No module named 'oauth2client'

TL;DR: oauth2client is dead upstream. Migrate the import to google-auth: service account code becomes google.oauth2.serviceaccount, and user OAuth becomes googleauth_oauthlib.flow. Pinning oauth2client is a stopgap at best.

ModuleNotFoundError: No module named 'oauth2client'

Fix it

1. Find the imports: grep -rn "oauth2client" your code. Expected: a short list.
2. Service accounts: replace from oauth2client.service_account import ServiceAccountCredentials with from google.oauth2 import service_account, and ServiceAccountCredentials.fromjsonkeyfilename(...) with serviceaccount.Credentials.fromserviceaccount_file(...). Expected: no oauth2client references left.
3. User OAuth: replace oauth2client.client.flowfromclientsecrets with googleauthoauthlib.flow.InstalledAppFlow.fromclientsecrets_file. Expected: the flow completes.
4. Install the new libs: pip install google-auth google-auth-oauthlib. Expected: imports succeed.

When this applies

• Your code or a dependency imports oauth2client.

When it doesn't

• Modern code already uses google-auth: this error means a stale dependency; upgrade it.
• You just need it running today: pip install oauth2client works but inherits unmaintained code.

Compatibility

• google-auth >= 1.0; Python 3.8+.

Why it happens

Google deprecated oauth2client in 2017 and archived it. New environments never have it, so legacy samples fail on import while modern ones work.

Edge cases

• Some old google-api-python-client versions still import oauth2client internally; upgrade google-api-python-client past 1.7.
• The credential JSON formats are compatible, so key files do not need regeneration.