Drivers on shapeKeys 2.8 issue

I have a following setup

I want to make one shape key depended on other shape key value
For some reson in my setup input value is always 0.

Is “Copy Data Path” in 2.8 not working correctly or did I miss something?

Also, I don’t know python and I can’t get the scripted expression right.
In JavaScript it would look like this :
1 - (Math.abs(var - 0.5) * 2)
Math.abs is absolute value in JS

I think ShapeKeys is bugged in 2.8 , check this topic.