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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 archive_namespace(self):
 """ Returns the known namespace of the RFC5005 extension, if any """

        try:
            for ns_prefix, url in self.feed.namespaces.items():
                if url == 'http://purl.org/syndication/history/1.0':
                    return ns_prefix
        except AttributeError:
            pass
        return None