The optimisations are around the javascript types, such as the number (float) and the object (which has string properties, a prototype chain, etc). Once you hav

The optimisations are around the javascript types, such as the number (float) and the object (which has string properties, a prototype chain, etc). Once you have to express all the Python semantics, like arbitrary precision integers or multiple inheritance, the optimisations no longer "skip" much of the work.