def unregister_filter(self, attr_name):
if attr_name not in self._filter_registry:<EOL><INDENT>raise NotRegistered(<EOL>'<STR_LIT>' % attr_name<EOL>)<EOL><DEDENT>else:<EOL><INDENT>del self._filter_registry[attr_name]<EOL><DEDENT>
Unregister the FilteredImage subclass currently assigned to attr_name.

If a FilteredImage subclass isn't already registered to filters.
`attr_name` NotRegistered will raise.