code: def access_token(self):
          
          access_token = self.session.get(self.access_token_key)
          if access_token:
              if not self.expires_at:
                  # user provided access_token, just return it
                  return access_token
  
              timestamp = time.time()
              if self.expires_at - timestamp > 60:
                  return access_token
  
          self.fetch_access_token()
          return self.session.get(self.access_token_key)
docs: WeChat access token