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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 on_scroll(self):
 """Called to scroll text"""

        try:
            sw = self.view['sw_scroller']
        except KeyError:
            return False # destroyed!        
        vadj = sw.get_vadjustment()
        if vadj is None: return False
        val = vadj.get_value()
        
        # is scrolling over?
        if val >= vadj.upper - vadj.page_size:
            self.view.show_vscrollbar()
            return False
        
        vadj.set_value(val+0.5)
        return True