[1718627440]

This is not just a performance concern, this describes completely different behaviour. You forgot that self.x is just Class.__getattr__(self, 'x') and that you can implement __getattr__ how you like. There is no object identity across the values returned by __getattr__.

[dundarious]

This level of dynamism is commonly forgotten/omitted because it is most often not at all needed. "There is no object identity across the values [retrieved by self.x]" is a very curious choice to many.

[1718627440]

It's very Pythonic to expose e.g. state via the existence of attributes. This also makes it possible to dynamically expose foreign language interfaces. You can really craft the interface you like, because the interface exposal is also normal code that returns strings and objects.

You are right that it is not needed often, but there is often somewhere a part in the library stack that does exactly this, to expose a nice interface.

[xenadu02]

This is just an analogy but in Swift String is such a commonly used hot path the type is designed to accommodate different backing representations in a performant way. The type has bits in its layout that indicate the backing storage. eg a constant string is just a pointer to the bytes in the binary and unless the String escapes or mutates incurs no heap allocation at all - it is just a stack allocation and a pointer.

Javascript implementations do their own magic since most objects aren't constantly mutating their prototypes or doing other fun things. They effectively fast-path property accesses and fallback if that assumption proves incorrect.

Couldn't python tag objects that don't need such dynamism (the vast majority) so it can take the fast path on them?

[adrian17]

It already has a fast path, from (I think) 3.11. If you run `object.x` repeatedly on the same type of object enough times, the interpreter will swap out the LOAD_ATTR opcode to `LOAD_ATTR_INSTANCE_VALUE` or `LOAD_ATTR_SLOT`, which only makes sure that the type is the same as before and loads the value from a specified offset, without doing a full lookup.