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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 _to_link_header(self, link):
 """ Convert the link tuple to a link header string. Used internally. """

        try:
            bucket, key, tag = link
        except ValueError:
            raise RiakError("Invalid link tuple %s" % link)
        tag = tag if tag is not None else bucket
        url = self.object_path(bucket, key)
        header = '<%s>; riaktag="%s"' % (url, tag)
        return header