Python is very developer productivity friendly, but degrades performance in weird ways and the methods to increase performance don't always make lots of obvious sense and often are the "idiomatic" way.

I haven't looked into the guts myself, but I'd bet that for similar or equivalent operations, the way the different syntaxes are handled under the hood are wildly different. e.g. function calls are much faster than method calls on objects.

Optimized pure python can look very ugly and non-idiomatic.