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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 __fetch_data(self, url):
 """ helper function for fetching data given a request URL """

        url += '&api_key=' + self.api_key
        try:
            response = urlopen(url)
            root = ET.fromstring(response.read())
        except HTTPError as exc:
            root = ET.fromstring(exc.read())
            raise ValueError(root.get('message'))
        return root