def METHOD_NAME(self, request):
    if request.get('PutRequest'):
        return [
            request['PutRequest']['Item'][key]
            for key in self._overwrite_by_pkeys
        ]
    elif request.get('DeleteRequest'):
        return [
            request['DeleteRequest']['Key'][key]
            for key in self._overwrite_by_pkeys
        ]
    return None