http://python-future.org/compatible_idioms.html?highlight=cmp#cmp recommends `cmp = lambda(x, y): (x > y) - (x < y)` but that is a SyntaxError in Python 3.6... `python3 -c 'cmp = lambda(x, y): (x > y) - (x < y)'` # --> SyntaxError What is the correct approach?