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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 history_size_changed(self, settings, key, user_data):
 """If the gconf var history_size be changed, this method will be called and will set the scrollback_lines property of all terminals open. """

        lines = settings.get_int(key)
        for i in self.guake.notebook_manager.iter_terminals():
            i.set_scrollback_lines(lines)