Unable to access tracks object in pyhton

[Exception4U]

i am unable to access 3d points in tracks

tried writting following code

    tracks = recon.getTracks()
    for i in tracks:
        print '3d points', i.pt.x, i.pt.y, i.pt.z
        pixels = recon.getTracksPixels(i)
        print i.pixels.size(),

but it did not work