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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 set_duration(self, rule):
 """Set the duration according to rule. rule: str The rule operating on the variable ``dur``. rule is an expression like:: setting a duration rule assuming a pack sp:: The identifier ``dur`` must be present or the rule will fail. .. note:: The logical ``or`` and ``and`` operators must be used. ``dur`` is a primitive, not an array. .. note:: Updates the mask if not no_auto. .. seealso:: :meth:`~channelpack.ChannelPack.set_samplerate` :meth:`~channelpack.ChannelPack.add_condition` :meth:`~channelpack.ChannelPack.pprint_conditions` """


        self.conconf.set_condition('duration', rule)
        if not self.no_auto:
            self.make_mask()