You can easily do regular checkerboards by using numpy to copy parts of an image (array) onto another array, like this:
# Let's define two arrays to work on. They should be replaced with your surfaces
a = numpy.ones((640,480))
b = numpy.zeros((640,480))
a[100:110,200:210] = b[100:110, 200:210]
Obviously you can mix it up, copy from multiple sources and different locations if you need it for your effects. Since everything is handled by numpy (without coming back to python after every pixel) it is quite fast.
The only limitation is that the source and destination must be the same size (or obey the broadcasting rules, but that's not what you want here).
I had completely forgotten about
choose(). It is the missing piece you need to do the transitions "properly". What you need is something like this:
diamonds = [ ... ] # List of arrays containing 1 and 2 arranged in enlarging diamond patterns, say 100x100
for diamond in diamonds: # you probably want timers and events rather than a tight loop
for x in [0,100,200, ...]:
for y in [0,100,200 ....]:
screen[x:x+100, y:y+100] = diamond.choose(screen1[x:x+100,y:y+100], screen2[x:x+100,y:y+100])
# Pause for transition effect
This should get you the required effect. Post if you get into trouble.