Flatten Nested List Iterator LeetCode solution in Python

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class NestedIterator:
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    def __init__(self, nestedList: [NestedInteger]):
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        self.flattened_lst = self.flattenList(nestedList)
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        self.idx = 0
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    def next(self) -> int:
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        if self.idx >= len(self.flattened_lst):
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            raise Exception("Index out of bound")
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        self.idx += 1
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        return self.flattened_lst[self.idx - 1]
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    def hasNext(self) -> bool:
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        return self.idx < len(self.flattened_lst)
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    def flattenList(self, lst):
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        flattened_lst = []
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        for ele in lst:
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            if ele.isInteger():
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                flattened_lst.append(ele.getInteger())
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            else:
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                flattened_lst.extend(self.flattenList(ele.getList()))
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        return flattened_lst