code: def access_token(self):
          
          if (self._access_token is None or
                  self.expiration_time <= int(time.time())):
              resp = self.make_access_request()
              self._access_token = resp.json()['access_token']
  
          return self._access_token
docs: Stores always valid OAuth2 access token.
  
          Note:
              Accessing this property may result in HTTP request.
  
          Returns:
              str