We definitely can't use a valid identifier in the code generator, since any valid identifier we used might shadow a nonlocal, global or builtin name (and the latter two cases aren't visible to the compiler at compile time).

They're also genuinely not positional only:

>>> print(setcomp_func(iter(range(5))))
{0, 1, 4, 9, 16}
>>> print(setcomp_func(**{".0": iter(range(5))}))
{0, 1, 4, 9, 16}