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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 etag(self, href):
 """ ETag can be None if a subset of element json is using this container, such as the case with Routing. """

        if self and self._etag is None:
            self._etag = LoadElement(href, only_etag=True)
        return self._etag