code: def flush(self, key=None):
          
  
          if not key is None:
              if key in self.data:
                  del self.data[key]
          else:
              self.data = {}
              self.next_cleaning = time.time() + self.cleaning_interval
docs: Flush the cache.
  
          If I{key} is specified, only that item is flushed.  Otherwise
          the entire cache is flushed.
  
          @param key: the key to flush
          @type key: (dns.name.Name, int, int) tuple or None