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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 create_backup(self):
 """Ask controller to create a backup archive file, response contains the path to the backup file. Warning: This process puts significant load on the controller may render it partially unresponsive for other requests. """


        js = json.dumps({'cmd': 'backup'})
        params = urllib.urlencode({'json': js})
        answer = self._read(self.api_url + 'cmd/system', params)

        return answer[0].get('url')