Thanks for the elaboration;
in retrospect, given the simple requirement, that there are only two
dict keys, one of which is know and the other to be determined, maybe
just the direct dict methods are appropriate, e.g.
d = {'a': 'bob', 'b': 'stu'}
d_copy = dict(d)
d_copy.pop("a")
'bob'
d_copy.popitem()
('b', 'stu')
vbr