RE: [Python-Dev] Change in evaluation order in new object model

[Michael McLay]

... The lookup of a member is also faster because it uses a lookup of an offset instead of a dictionary lookup.

There's still a dict lookup: when you do obj.a where a is a __slot__ attribute of obj.__class__, obj.__class__.__dict__['a'] is looked up in order to get the descriptor for attribute 'a'. The fixed set of __slot__ attributes leaves a door open for future optimizations, though (e.g., if Python could *know* obj.__class__ at compile-time, and know that runtime code won't overwrite the 'a' descriptor in obj.__class__.__dict__, it could map obj.a directly to its storage offset (from the base of obj) at compile-time).