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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 get_average_cross_validation_fitness(self):
 # pragma: no cover """Get the per-generation average cross_validation fitness."""

        avg_cross_validation_fitness = []
        for stats in self.generation_cross_validation_statistics:
            scores = []
            for fitness in stats.values():
                scores.extend(fitness)
            avg_cross_validation_fitness.append(mean(scores))

        return avg_cross_validation_fitness