def check_version(self):
        """Raise ValueError if the version for this interface
        does not match any of the versions given for the API.
        """
        uri = urljoin(self.baseuri, 'api')
        r = requests.get(uri, auth=(self.username, self.password))
        root = self.parse_response(r)
        tag = nsmap('ver:versions')
        assert tag == root.tag
        for node in root.findall('version'):
            if node.attrib['major'] == self.VERSION: return
        raise ValueError('version mismatch')