code: def get_default_session(self):
          
          if self._sessions:
              return self.get_session(next(iter(self._sessions)))
          return self.get_session()
docs: The default session is nothing more than the first session added
          into the session handler pool. This will likely change in the future
          but for now each session identifies the domain and also manages
          domain switching within a single session.
          
          :rtype: Session