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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 unregisterMachine(self, machineName):
 """ This operation unregisters a portal machine from a portal site. The operation can only performed when there are two machines participating in a portal site. """

        url = self._url + "/machines/unregister"
        params = {
            "f" : "json",
            "machineName" : machineName
        }
        return self._post(url=url,
                          param_dict=params,
                          proxy_url=self._proxy_url,
                          proxy_port=self._proxy_port)