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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 joinSite(self, machineAdminUrl, username, password):
 """ The joinSite operation connects a portal machine to an existing site. You must provide an account with administrative privileges to the site for the operation to be successful. """

        params = {
            "machineAdminUrl" : machineAdminUrl,
            "username" : username,
            "password" : password,
            "f" : "json"
        }
        url = self._url + "/joinSite"
        return self._post(url=url, param_dict=params)