learning shape key tools on simple robot face

Hi,
this is a simple example i wrote that explores scripting creation of shape keys and making sliders for them in blender 2.79.  it creates shape keys for two brows and mouth simple plane meshes.  i'm still learning blender so there may be better approaches to scripting this.

test blender file for robot face:blender 2.79 file




hope you find this helpful,
Happy Scripting and Sketching!
Nate