It's ok to __slots__ for what they were intended (was: Don't use __slots__ (was Re: Why custom objects take so much memory?))

[Chris Mellon]

On 20 Dec 2007 19:50:31 -0800, Aahz <aahz at pythoncraft.com> wrote:
> In article <0829587b-f3a1-4f77-86a1-163e7bcc54d2 at l32g2000hse.googlegroups.com>,
> Carl Banks  <pavlovevidence at gmail.com> wrote:
> >On Dec 18, 4:49 pm, a... at pythoncraft.com (Aahz) wrote:
> >> In article <mailman.2538.1198008758.13605.python-l... at python.org>,
> >> Chris Mellon <arka... at gmail.com> wrote:
> >>>
> >>>You can reduce the size of new-style classes (inherit from object) by
> >>>quite a bit if you use __slots__ to eliminate the class dictionary.
> >>
> >> You can also reduce your functionality quite a bit by using __slots__.
> >> Someday I'll have time to write up a proper page about why you shouldn't
> >> use __slots__....
> >
> >Shouting absolute commands without full understanding of the situation
> >is not going to help anyone.
>
> Maybe not, but at least it will get people to stop for a bit.
>

No, it will just make people stop ignoring you because you give
inappropriate advice forbidding reasonable solutions without a
rational justification.

> >The OP wanted to minimize memory usage, exactly the intended usage of
> >slots.  Without knowing more about the OP's situation, I don't think
> >your or I or Chris Mellon can be sure it's not right for the OP's
> >situation.
>
> The whole point about warning against __slots__ is that you should never
> use them unless you are certain they're the best solution.  Consider what
> happens when the OP wants to subclass this __slots__-using class.

Nothing. Subclasses of a class with __slots__ get a dict just like
anything else, unless they also define slots. Why do you think you can
subclass object to get something you can stick arbitrary attributes
on?

> Avoiding __slots__ will almost never harm anyone, so I feel completely
> comfortable sticking with a blanket warning.
> --

Barking out your blanket warning in a thread on *the exact use case
slots were implemented to address* just makes you look like a mindless
reactionary. Stick to posting your warning in threads where people ask
how to stop "other people" from setting attributes on "their"
instances.