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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_default_field_names(self, declared_fields, model_info):
 """ Return default field names for serializer. """

        return (
            [model_info.pk.name] +
            list(declared_fields.keys()) +
            list(model_info.fields.keys()) +
            list(model_info.relations.keys())
        )