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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 add_missing(self, aesthetics):
 """ Add missing but required scales. Parameters aesthetics : list | tuple Aesthetic names. Typically, ('x', 'y'). """

        # Keep only aesthetics that don't have scales
        aesthetics = set(aesthetics) - set(self.input())

        for ae in aesthetics:
            scale_name = 'scale_{}_continuous'.format(ae)
            scale_f = Registry[scale_name]
            self.append(scale_f())