The idiom that I'm aware of and that I follow is to create a mixin class and add the word `Mixin` at the end of the class. E.g.

```
class ThumbnailMakerMixin(object):
    def generate_thumbnail(self, size):
         im = Image.open(self.file_path)
         im = im.thumbnail(size)
         im.save(self.save_file_path)
```

But I didn't read that in some bless documentation. Just something I've learned from observation.