I'm not sure I understand this question.

Gating this block with PyObject_CheckBuffer is an exact check on obj.type == buffer,
which precludes the set of exact types, or am I missing something?

Also, in ctor.c a similar block is checked for PY_VERSION_HEX>=02060000 as is the
case in numpy.1.7.1 on my machine for common.c.  Why was the ##if test removed from
common.c?