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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 move_item_up(self, item):
 """Move an item up in the list. Essentially swap it with the item above it. :param item: The item to be moved. """

        prev_iter = self._prev_iter_for(item)
        if prev_iter is not None:
            self.model.swap(prev_iter, self._iter_for(item))