IK on/off switch between hand and arm that affects elbow

I’ve been trying to make an armature that has IK constraints on both the lower arm and the hand, but that where both constraints also have an on/off switch. My intent is to never have the IK switch both the hand and lower arm on simultaneously. If both switches are off, the whole arm acts with FK. The problem I’ve been having is trying to get the switches to affect the elbow control. I have the elbow control set up by having an IK constraint on the upper arm and targeting it to a free floating bone.

I tried using a PyDriver but I was unable to fit enough characters in the textbox to write it. I tried to write the following script:


I’d really rather not have to shrink the names of bones because then they are less descriptive and it is harder to figure out which bone does what.

I’ve thought about using a PyConstraint, but it looks like that can only access the object’s loc/rot/scale matrix and not influence values for a constraint.

In addition, I’m not really sure if the way I set up the elbow control is the best way to do it.