The number crunching part is already fast enough, however the aggregations, parsing and filtering that come beforehand is really really slow. This part is often

The number crunching part is already fast enough, however the aggregations, parsing and filtering that come beforehand is really really slow. This part is often done in pure python because it's often custom code tailored to the data you're manipulating. We're not interested in scaling up the parts that are already fast, but the rather mundane, uninteresting work that come before.