Hi, This mail is the consequence of a true story, a story where CPython got defeated by Javascript, Java, C# and Go. One of the teams of the company where Im working had a kind of benchmark to compare the different languages on top of their respective "official" web servers such as Node.js, Aiohttp, Dropwizard and so on. The test by itself was pretty simple and tried to test the happy path of the logic, a piece of code that fetches N rules from another system and then apply them to X whatevers also fetched from another system, something like that def filter(rule, whatever): if rule.x in whatever.x: return True rules = get_rules() whatevers = get_whatevers() for rule in rules: for whatever in whatevers: if filter(rule, whatever): cnt = cnt + 1 return cnt The performance of Python compared with the other languages was almost x10 times slower. It's true that they didn't optimize the code, but they did not for any language having for all of them the same cost in terms of iterations. Once I saw the code I proposed a pair of changes, remove the call to the filter function making it "inline" and caching the rule's attributes, something like that for rule in rules: x = rule.x for whatever in whatevers: if x in whatever.x: cnt += 1 The performance of the CPython boosted x3/x4 just doing these "silly" things. The case of the rule cache IMHO is very striking, we have plenty examples in many repositories where the caching of none local variables is a widely used pattern, why hasn't been considered a way to do it implicitly and by default? The case of the slowness to call functions in CPython is quite recurrent and looks like its an unsolved problem at all. Sure I'm missing many things, and I do not have all of the information. This mail wants to get all of this information that might help me to understand why we are here - CPython - regarding this two slow patterns. This could be considered an unimportant thing, but its more relevant than someone could expect, at least IMHO. If the default code that you can write in a language is by default slow and exists an alternative to make it faster, this language is doing something wrong. BTW: pypy looks like is immunized [1] [1] https://gist.github.com/pfreixes/d60d00761093c3bdaf29da025a004582 -- --pau