Thanks Matti. I agree that it would be good to have an automated check for these.

have you tested this locally? when i tried this in cython/cython#3606 i found i needed to use PyObject* rather than object for the fourth arg

No I did not, in fact we only consume cython internally in the random module.

I guess backing this PR out will not really solve the problem: the signature will still be wrong

How come the difference? To be able to pass NULL? I always get a bit confused, in the signature that does not have an effect on the reference counts does it?

@scoder See #16720.

in the signature that does not have an effect on the reference counts does it?

No, it's an input argument, so the ref-count does not change. However, an object cannot be NULL, because that signals an exception and therefore Cython does not allow object arguments to be NULL. You have to use PyObject* here to allow the argument "not to be passed".