code: def get(self, request_url):
          
          try:
              cached_item = self._table[request_url]
              cur_time = timeutils.now('unix')
              if cur_time - cached_item['insertion_time'] > self._item_lifetime:
                  # Cache item has expired
                  self._clean_item(request_url)
                  return None
              cached_item['insertion_time'] = cur_time  # Update insertion time
              self._promote(request_url)
              return cached_item['data']
          except:
              return None
docs: In case of a hit, returns the JSON string which represents the OWM web
          API response to the request being identified by a specific string URL
          and updates the recency of this request.
  
          :param request_url: an URL that uniquely identifies the request whose
              response is to be looked up
          :type request_url: str
          :returns: a JSON str in case of cache hit or ``None`` otherwise