def _set_thumbnail(self, instance=None, **kwargs):
image_field = getattr(instance, self.name)<EOL>if image_field:<EOL><INDENT>thumbnail_filename = _get_thumbnail_filename(image_field.name)<EOL>thumbnail_field = ThumbnailField(thumbnail_filename, self.storage)<EOL>setattr(image_field, '<STR_LIT>', thumbnail_field)<EOL><DEDENT>
Sets a `thumbnail` attribute on the image field class.
On thumbnail you can access name, url, path attributes