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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 _iterate(self, data, expanded_data):
 """ _Iterate through all data, store the result expansion in extended dictionary """

        for attribute in SOURCE_KEYS:
            for k, v in data[attribute].items():
                if k == None:
                    group = 'Sources'
                else:
                    group = k
                if group in data[attribute].keys():
                    self._expand_data(data[attribute][group], expanded_data, group)
        for k, v in data['include_files'].items():
            if k == None:
                group = 'Includes'
            else:
                group = k
            self._expand_data(data['include_files'][group], expanded_data, group)

        # sort groups
        expanded_data['groups'] = OrderedDict(sorted(expanded_data['groups'].items(), key=lambda t: t[0]))