You even get an informative message like:
a, b, c, d = someList
# -->
# Unhandled Exception: Cobra.Core.UnpackException: Cannot unpack 3 values into 4 targets.
Take it for a spin and let me know if you have any feedback.
The ticket:
http://cobra-language.com/trac/cobra/ticket/284
The changeset:
http://cobra-language.com/trac/cobra/changeset/2746