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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 flatten(self):
 """ Get a flattened list of the items in the collection. :rtype: Collection """


        def _flatten(d):
            if isinstance(d, dict):
                for v in d.values():
                    for nested_v in _flatten(v):
                        yield nested_v
            elif isinstance(d, list):
                for list_v in d:
                    for nested_v in _flatten(list_v):
                        yield nested_v
            else:
                yield d

        return self.__class__(list(_flatten(self.items)))