my use case is different (I do a loop), but what I expected from the docs (just for fun!)

class Ddefault:

    def __init__(self):
        vars(self).setdefault('default', self.set_default() if not 'default' in vars(self) else self.default)
        vars(self).setdefault('default', self.set_default() if not 'default' in vars(self) else self.default)
        print(vars(self))

    def set_default(self):
        print(vars(self))
        return 'default'

if __name__ == "__main__":
    Ddefault()

may be the coding diverted from the docs after the fixing of issue 13521 and no one dares correcting..
anyway, I will probably keep my old coding (performance, if there is any)