While I was backporting the new buffer API to 2.7 I noticed some issues 
in array_ass_slice() in Modules/arraymodule.c in the python 3k branch.

1) Manual memory reallocation had been replaced by calls to 
array_resize. But I think when PyMem_RESIZE is called the pointer to the 
memory might change. So this now happens in array_resize, and the
array->ob_item pointer changes but not it's local copy (item) in 
array_ass_slice().

2) The function moves too much memory if the array size is increased: 
(Py_SIZE(a)-d-ihigh) items should be moved, because Py_SIZE(a) was 
already modified by array_resize, but the function moves (Py_SIZE(a)-
ihigh) items.

While 1) might go unnoticed, 2) definitely broke slice tests in a 
"segmentation fault"-way (in debug mode forbidden bits show the error). 
I tried to write a test, but I don't know how to trigger 
array_ass_slice() with a write access, as it is not in array_as_sequence 
anymore (like in 2.7). How is slicing handled now?

The array type also defines tp_as_mapping->mp_ass_subscript, which has
priority in PyObject_SetItem().
A way to call array_ass_slice() is to use PySequence_SetItem(), but this
is hard to trigger from python code (it should be possible with ctypes).

The mp_ass_subscript function looks fine in contrast to array_ass_slice(). 
So if array_ass_slice() is not accessible from the outside and is only 
called with NULL as replacement parameter from the inside, I won't be able 
to cause trouble with those two issues.

Still I think it's bad to keep buggy code around, even it is not used. 
Maybe array_ass_slice() should be changed to what it's used for: 
array_del_slice()?