I had a similar problem creating a C-fast array.array interface for Cython.
The array.pxd package here (latest zip file)
http://trac.cython.org/cython_trac/ticket/314
includes a arrayarray.h file, which provides ways for efficient creation
and growth from C (extend, extend_buffer, resize, resize_smart ). Its
probably in one of the next Cython distributions anyway, and will be
maintained. And perhaps array2 and arrayM extension subclasses (very
light-weight numpy) with public API coming soon too.
It respects the different Python versions, so its a lite "quasi API".
And in case there will be a (unlikely) change in future Pythons, the
Cython people will take care as far as there is no official API coming up.
Or perhaps most people with such interest use Cython anyway.