> Wide build:
>>>> memoryview(array("u")).format
> 'w'
>
> Narrow build:
>>>> memoryview(array("u")).format
> 'u'
>
> Neither of these are valid struct formats, thus they don't play
> nicely with the assumptions of memoryview (or any other PEP 3118
> consumer).

Why do you say that? They have been added by PEP 3118 (and are
just not implemented in the struct module yet).

If you think that their mentioning in PEP 3118 is a mistake,
and they should not get implemented in struct, we should
a) get consensus on that interpretation of the PEP, and
b) actually remove them from the PEP, since otherwise it
    is very confusing that they keep being mentioned.
I believe that the addition of these codes was fully
intended by the PEP author, and also part of its acceptance.

If these codes are indeed meant to be in the struct module,
this usage in the array module looks right to me - hence
my proposal to close the issue (the documentation problem
aside).

I agree that it is then desirable that the memoryview object
supports the codes. However, this is separate issue from this
one (as the codes are not invalid, just unsupported).