Comment by cpburns2009
19 hours ago
I've never bought this argument. Underneath all of the magic inheritance in Python is just the MRO (method resolution order). That's not characteristically any different from JavaScript's prototype chain. There's no reason a Python JIT couldn't optimize everything JavaScript does, and if you do specifically access `self.__dict__`, that can be a cold, unoptimizable path.
One of the tricks here is to treat the happy path as a quasi-invariant and leave a guard that branches to slow code if the invariant didn’t hold.
I saw this presented as new tech at either OOPSLA or OSCon almost exactly 20 years ago.
CPU branch prediction is still pretty good even with the loss of function in recent years.
That works fine as long as nobody actually uses the unhappy path. If major libraries and frameworks do it all the time, you lose. So there is a certain aspect of culture outside what the language itself is capable of doing.
I'd say that's about right. The way people usually code in Python, mro is quite stable and most lookups would be cache hits. You can still get more weird invalidation in Python cuz they let you change stuff like `__bases__`, or you get some weird `__getattribute__` change in some place that would force you to invalidate more than you'd initially think should be necessary.