Convert a ctypes int pointer array to a numpy array.

def cint32_array_to_numpy(cptr, length):
    """Convert a ctypes int pointer array to a numpy array."""
    if isinstance(cptr, ctypes.POINTER(ctypes.c_int32)):
        return np.fromiter(cptr, dtype=np.int32, count=length)
    else:
        raise RuntimeError('Expected int pointer')