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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 get_uvi(self, params_dict):
 """ Invokes the UV Index endpoint :param params_dict: dict of parameters :returns: a string containing raw JSON data :raises: *ValueError*, *APICallError* """

        lat = str(params_dict['lat'])
        lon = str(params_dict['lon'])
        params = dict(lat=lat, lon=lon)

        # build request URL
        uri = http_client.HttpClient.to_url(UV_INDEX_URL, self._API_key, None)
        _, json_data = self._client.cacheable_get_json(uri, params=params)
        return json_data