(beginners question) howto set self.field4.subfield8='asdf'?

[openopt at ukr.net]

I have
class A:
def __init__(self, objFun, x0):
        #(I want to have self.primal.f = objFun)
        #both
        self.primal.f = objFun
        #and
        self.primal = None
        self.primal.f = objFun

yields error
what should I do?
Thx