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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 tagged_item_key(self, key):
 """ Get a fully qualified key for a tagged item. :param key: The cache key :type key: str :rtype: str """

        return '%s:%s' % (hashlib.sha1(encode(self._tags.get_namespace())).hexdigest(), key)