f['ext'] = determine_ext(f['url'])
if isinstance(field_preference, (list, tuple)):
- return tuple(f.get(field) if f.get(field) is not None else -1 for field in field_preference)
+ return tuple(
+ f.get(field)
+ if f.get(field) is not None
+ else ('' if field == 'format_id' else -1)
+ for field in field_preference)
preference = f.get('preference')
if preference is None: