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class PeekingIterator:
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    def __init__(self, iterator):
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        self.iterator = iterator
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        self.buffer = self.iterator.next() if self.iterator.hasNext() else None
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    def peek(self):
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        return self.buffer
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    def next(self):
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        tmp = self.buffer
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        self.buffer = self.iterator.next() if self.iterator.hasNext() else None
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        return tmp
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    def hasNext(self):
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        return self.buffer != None