def save(self, filename,  metadata={}, **data):
intersection = set(metadata.keys()) & set(data.keys())<EOL>if intersection:<EOL><INDENT>msg = '<STR_LIT>'<EOL>raise Exception(msg  % '<STR_LIT:U+002C>'.join(intersection))<EOL><DEDENT>
The implementation in the base class simply checks there is no
clash between the metadata and data keys.