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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 fetch_objects(self, oids):
        '''
        This methods is used to fetch models
        from a list of identifiers.

        Default implementation performs a bulk query on identifiers.

        Override this method to customize the objects retrieval.
        '''
        objects = self.model.objects.in_bulk(oids)
        if len(objects.keys()) != len(oids):
            non_existants = set(oids) - set(objects.keys())
            msg = _('Unknown identifiers: {identifiers}').format(
                identifiers=', '.join(str(ne) for ne in non_existants))
            raise validators.ValidationError(msg)

        return [objects[id] for id in oids]