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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def get(self, request_url):
 """ 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 """

        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