code: def _load_from_cache_if_available(self, key):
      
      if key in self._cache:
        entity = self._cache[key]  # May be None, meaning "doesn't exist".
        if entity is None or entity._key == key:
          # If entity's key didn't change later, it is ok.
          # See issue 13.  http://goo.gl/jxjOP
          raise tasklets.Return(entity)
docs: Returns a cached Model instance given the entity key if available.
  
      Args:
        key: Key instance.
  
      Returns:
        A Model instance if the key exists in the cache.