Yes, there was a plan - but I was thinking it would get a bit ugly to do this for deeply nested attributes like these.  I guess it would look something like:

op = self.frames[0].get('PlaneOrientationSequence')[0].get('ImageOrientationPatient')

I suppose we could do that - but the tests look OK to me with the class Fake(object) approach - so maybe it isn't worth it here - what do you think?