leetcode 284. Peeking Iterator

class PeekingIterator(object):    def __init__(self, iterator):        """        Initialize your data structure here.        :type iterator: Iterator        """        self.iter = iterator        self.buffer = self.iter.next() if self.iter.hasNext() else None    def peek(self):        """        Returns the next element in the iteration without advancing the iterator.        :rtype: int        """        return self.buffer    def next(self):        """        :rtype: int        """        res = self.buffer        self.buffer = self.iter.next() if self.iter.hasNext() else None        return res            def hasNext(self):        """        :rtype: bool        """        return self.buffer is not None