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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 stack_suffix(self, context_sensitivity_level):
 """ Generate the stack suffix. A stack suffix can be used as the key to a SimRun in CFG recovery. :param int context_sensitivity_level: Level of context sensitivity. :return: A tuple of stack suffix. :rtype: tuple """


        ret = ()

        for frame in self:
            if len(ret) >= context_sensitivity_level*2:
                break
            ret = (frame.call_site_addr, frame.func_addr) + ret

        while len(ret) < context_sensitivity_level*2:
            ret = (None, None) + ret

        return ret