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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_dimmer(self, dimmer, transition_time=None):
 """Set dimmer value of a group. dimmer: Integer between 0..255 transition_time: Integer representing tenth of a second (default None) """

        values = {
            ATTR_LIGHT_DIMMER: dimmer,
        }
        if transition_time is not None:
            values[ATTR_TRANSITION_TIME] = transition_time
        return self.set_values(values)