As I mentioned in a comment on Jaime's response (https://wrongsideofmemphis.wordpress.com/2015/05/08/optimise...), we actually do quite a bit more than this in our production code. The blog post here is meant to demonstrate the point, not to show our exact production code.

In particular, I wanted all 3 examples to use nearly identical inside the filter function, to isolate the differences just between the ways of accessing data in the benchmark results, and to show that closures are an easy way to gain some performance in hot spots (in CPython at least).