code: def Items(self, key):
      
      with self._mutex:
        if key not in self._buckets:
          raise KeyError('Key %s was not found in Reservoir' % key)
        bucket = self._buckets[key]
      return bucket.Items()
docs: Return items associated with given key.
  
      Args:
        key: The key for which we are finding associated items.
  
      Raises:
        KeyError: If the key is not found in the reservoir.
  
      Returns:
        [list, of, items] associated with that key.