Mutable objects?

[Alex Martelli]

Magnus Lie Hetland wrote:

> Just wondering... Would it be possible for object() to return a
> mutable instance, sort of instances of
> 
>   class Object: pass
> 
> or something?
> 
> (I'm sure this violates some sort of internal logic; it just seems
> sort of useful when you just need a generic object...)

If any instance of object has a __dict__ then we lose the memory
savings of having __slots__ (and pay for a __dict__ in every
object... nightmarish, as that __dict__ also is-a object...!).

If a direct instance of object has a __dict__ but an indirect one
may or may not have it we're breaking one of the most fundamental
tenets of inheritance (subclassing): subclassing doesn't remove stuff.

If instances of object don't necessarily have a __dict__, what kind
of "mutability" can we use on them?

"Seems sort of useful" is weakish motivation for facing these very
thorny issues, it seems to me.  I don't look at them as "some sort
of internal logic", having to do with mere implementation issues, but
as part and parcel of my mental model of how Python works.


Alex