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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 push(self, item):
 """ Push and item onto the sorting stack. @param item: An item to push. @type item: I{item} @return: The number of items pushed. @rtype: int """

        if item in self.pushed:
            return
        frame = (item, iter(item[1]))
        self.stack.append(frame)
        self.pushed.add(item)