Download the below library it supporting 2legged oauth
google-api-python-client==1.0beta4
and make sure your manifest contains updated calendar(v3) scopes then
from apiclient.oauth import TwoLeggedOAuthCredentials
from apiclient.discovery import build
import httplib2
credentials = TwoLeggedOAuthCredentials(OAUTH_CONSUMER_KEY,OAUTH_CONSUMER_SECRET,'referer')
credentials.requestor = user_email
http = httplib2.Http()
http = credentials.authorize(http)
calendar_service = build('calendar', 'v3', http=http)
list = calendar_service.events().list(calendarId="primary").execute()