decorator to prevent adding attributes to class?

[Neal Becker]

After spending the morning debugging where I had misspelled the name of an
attribute (thus adding a new attr instead of updating an existing one), I
would like a way to decorate a class so that attributes cannot be (easily)
added.

I guess class decorators are not available yet (pep 3129), but probably
inheritance can be used.

Can anyone suggest an implementation?