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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_related(self, instance, number):
 """ Implement high level cache system for get_related. """

        cache = self.cache
        cache_key = '%s:%s' % (instance.pk, number)
        if cache_key not in cache:
            related_objects = super(CachedModelVectorBuilder,
                                    self).get_related(instance, number)
            cache[cache_key] = related_objects
            self.cache = cache
        return cache[cache_key]