Now, implement the following changes:

Change NUM_TARGETS to 2 instead of 1.
Add:   

    # Get the rotation for inner and outer gears.
     
    sunrot = targetmatrices[0].toEuler()
    outrot = targetmatrices[1].toEuler()

    # Get the position of the gear itself.
     
    localrot = obrot.z
         
    offsetx = (0 - obloc.x)
    offsety = (0 - obloc.y)
     
    globalrot = 0
     
    offset = math.sqrt((offsetx * offsetx) + (offsety * offsety))
     
    # Apply sun movement to temp values.
     
    globalrot += sunrot.z
     
    localrot += (1 - (sunrot.z * 3))
     
    # Apply outer movement to temp values.
     
    globalrot += outrot.z
     
    localrot += (outrot.z * 3)
     
    # Apply temp values to owner.
     
    obloc.y = (offset * math.sin((globalrot/180) * math.pi))
    obloc.x = (offset * math.cos((globalrot/180) * math.pi))
     
    obrot.z = localrot


After the "Do stuff here" comment. This will work for the first gear only, you will need to change the trig function maths for each individual gear. My actual file has four different pyconstraints.
Add two circles and a plane. Delete the faces on the circles and plane. Make the circles children of the plane, and lock their location, scale, and x and y rotation. Give the outer and sun gears transform constraints to rotate them the right number of times to line them up with the planets. You'll need to experiment with this one.
Finally, add a script constraint to each gear and select the correct script for the gear. Set all "spaces" to local, enter the circle which is controlling the sun as the first target, and the circle for the outer gear as the second target.

That's all! If you didn't get anything, feel free to comment or lay down a post at the blenderartists thread.