def METHOD_NAME(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)