I think it is not too unzen in its aim and method but if you ask there many little tricks that I'd say are unzen. First, give all the code a pass of autopep8 comb. Second, avoid things like "lambda (op,num): (num, -num)[...], just use "x if y else z"

Then you wouldn't be too far from Norvig's little educational gems.

I suppose I got carried away with the lambdas :)

Thank you, you gave me a great compliment. Norvig's short spellchecker was very inspirational for me.