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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 clean(self):
        '''Fill metrics with defaults on create'''
        if not self.metrics:
            self.metrics = dict(
                (name, spec.default)
                for name, spec in (metric_catalog.get(self.__class__, {})
                                                 .items()))
        return super(WithMetrics, self).clean()