[Python-Dev] Dinamically set __call__ method

Ian Kelly ian.g.kelly at gmail.com
Wed Nov 12 19:58:53 CET 2014


On Wed, Nov 12, 2014 at 8:33 AM, Fabio Zadrozny <fabiofz at gmail.com> wrote:
> As a reference, I recently found a blog post related to that:
> http://lucumr.pocoo.org/2014/8/16/the-python-i-would-like-to-see/ (the Slots
> part comments on that).
>
> It does seem a bit counter-intuitive that this happens the way it does
> though, so, can someone from python-dev give some background of why that's
> the way it is? i.e.: instead of the approach which would seem simpler which
> would do getattr(a, '__call__') instead of
> type(a).__dict__['__call__'].__get__(a, type(a)) -- it seems to me it's
> mostly because of historical reasons, but I'm really curious why is it so
> (and if maybe it's something which python-dev would consider worth changing
> in the future -- not sure how much could break because of that though).

I'm not "someone from python-dev", but I think it's done to keep the
look-up logic predictable and avoid having to call __getattribute__
and __getattr__ when looking up magic methods. For at least
__getattribute__ and __getattr__ themselves we *can't* invoke those
methods while trying to look them up, so there's a case to be made for
consistency in that this way we don't have to remember which magic
methods use __getattribute__ and which ones don't. Performance is also
part of it, since these methods tend to be invoked frequently.



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