code: def selenium(self):
          
          if not self._web_driver:
              self._web_driver = self._start_driver()
          return self._web_driver
docs: Get the instance of webdriver, it starts the browser if the
          webdriver is not yet instantied
  
          :return: a `selenium instance <http://selenium-python.readthedocs.org/
          api.html#module-selenium.webdriver.remote.webdriver>`