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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_up(self):
 """Move up one level in the hierarchy, unless already on top."""

        if self.current_item.parent is not None:
            self.current_item = self.current_item.parent

        for f in self._hooks["up"]:
            f(self)
        if self.current_item is self.root:
            for f in self._hooks["top"]:
                f(self)
        return self