def _load_identifiers(self, attrs, meta, resource_model, resource_name):
        """
        Populate required identifiers. These are arguments without which
        the resource cannot be used. Identifiers become arguments for
        operations on the resource.
        """
        for identifier in resource_model.identifiers:
            meta.identifiers.append(identifier.name)
            attrs[identifier.name] = self._create_identifier(
                identifier, resource_name
            )

        Populate required identifiers. These are arguments without which
        the resource cannot be used. Identifiers become arguments for
        operations on the resource.
        
boto3/resources/factory.py