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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 update(self, old, new):
 """Replace an element in the heap """

        i = self.rank[old]     # change value at index i
        del self.rank[old]
        self.heap[i] = new
        self.rank[new] = i
        if old < new:          # maintain heap order
            self.down(i)
        else:
            self.up(i)