code: def _get_path_pattern_tornado4(self):
          
          for host, handlers in self.application.handlers:
              if host.match(self.request.host):
                  for handler in handlers:
                      if handler.regex.match(self.request.path):
                          return handler.regex.pattern
docs: Return the path pattern used when routing a request. (Tornado<4.5)
  
          :rtype: str