"Unit tester" for Google Auth Library (Python) Bug 501

bug501.py

# https://github.com/googleapis/google-auth-library-python/issues/501

from __future__ import print_function
import os
from google.oauth2 import credentials

TOKENS = 'tokens.json' # OAuth2 token storage
if  os.path.exists(TOKENS):
    creds = credentials.Credentials.from_authorized_user_file(TOKENS)
if not (creds and creds.valid):
    if creds and creds.expired and creds.refresh_token:
        print('** Auto-refresh: got creds? [%s], valid? [%s], expired? [%s]' % (
                bool(creds), creds.valid, creds.expired))
    else:
        print('** Re-run flow: creds [%s], valid? [%s], expired [%s]' % (
                bool(creds), creds.valid, creds.expired))
else:
    print('** "Valid" creds: creds [%s], valid? [%s], expired [%s]' % (
                bool(creds), creds.valid, creds.expired))