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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 _set_up_reference_fields(new_class):
 """Walk through relation fields and setup shadow attributes"""

        if new_class.meta_.declared_fields:
            for _, field in new_class.meta_.declared_fields.items():
                if isinstance(field, Reference):
                    shadow_field_name, shadow_field = field.get_shadow_field()
                    setattr(new_class, shadow_field_name, shadow_field)
                    shadow_field.__set_name__(new_class, shadow_field_name)