def is_(xxx_todo_changeme):
    (pbc1, pbc2) = xxx_todo_changeme
    thistype = pairtype(SomePBC, SomePBC)
s = super(thistype, pair(pbc1, pbc2)).is_()
if not s.is_constant():
    if not pbc1.can_be_None or not pbc2.can_be_None:
        for desc in pbc1.descriptions:
            if desc in pbc2.descriptions:
                break
else:
    s.const = False
return s
Pythonic способы использования else в цикле for