Error handling in requests
            http://api.yandex.ru/cleanweb/doc/dg/concepts/error-codes.xml

def request(self, *args, **kwargs):
        """ Error handling in requests
            http://api.yandex.ru/cleanweb/doc/dg/concepts/error-codes.xml
        """
        r = self.session.request(*args, **kwargs)
        if r.status_code != requests.codes.ok:
            error = ET.fromstring(r.content)
            message = error.findtext('message')
            code = error.attrib['key']
            raise CleanwebError('%s (%s)' % (message, code))
        return r