PyOpenCL not working correctly on OS X, no output

Question

I am trying to get PyOpenCL working on my iMac running Mac OS X Lion with NumPy 1.5.1 and Python 2.6.0. I have installed PyOpenCL first using easy_install and then I tried how it is explained here: http://wiki.tiker.net/PyOpenCL/Installation/Mac

When I run the demo script (http://documen.tician.de/pyopencl/#), it shows the OpenCL devices (Intel Core i3 and ATI Radeon HD5670), but when I choose one of two, both print 0.0

    Choose device(s):
[0] <pyopencl.Device 'Intel(R) Core(TM) i3 CPU         550  @ 3.20GHz' on 'Apple' at 0xffffffff>
[1] <pyopencl.Device 'ATI Radeon HD 5670' on 'Apple' at 0x1021b00>
Choice, comma-separated [0]:1
Set the environment variable PYOPENCL_CTX='1' to avoid being asked again.
0.0

What is going wrong here? Thanks in advance!

Answer 1

At the end of the script:

print la.norm(a_plus_b - (a+b))

So 0.0 is the expected returned value if everything went fine...