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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 addToDefinition(self, json_dict):
 """ The addToDefinition operation supports adding a definition property to a hosted feature service. The result of this operation is a response indicating success or failure with error code and description. This function will allow users to change add additional values to an already published service. Input: json_dict - part to add to host service. The part format can be derived from the asDictionary property. For layer level modifications, run updates on each individual feature service layer object. Output: JSON message as dictionary """

        params = {
            "f" : "json",
            "addToDefinition" : json.dumps(json_dict),
            "async" : False
        }
        uURL = self._url + "/addToDefinition"
        res = self._post(url=uURL, param_dict=params,
                             securityHandler=self._securityHandler,
                             proxy_port=self._proxy_port,
                             proxy_url=self._proxy_url)
        self.refresh()
        return res