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From: Ian Kelly <ian.g.kelly@gmail.com>
Newsgroups: comp.lang.python
Subject: Re: Lost in descriptor land
Date: Sat, 2 Jul 2016 17:06:47 -0600
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Xref: csiph.com comp.lang.python:110965

On Sat, Jul 2, 2016 at 5:32 AM, Ankush Thakur <ankush.thakur53@gmail.com> w=
rote:
> On Friday, July 1, 2016 at 9:13:19 AM UTC+5:30, Lawrence D=E2=80=99Olivei=
ro wrote:
>>
>> > Shouldn't we be instead using self.celcius in, say, __init__() and the=
n
>> > everything will work fine?
>>
>> I guess it might. But this way, using descriptors, all the setup is done=
 once at class definition, rather then every time in class instantiation.
>
> So you're saying the (sole) reason to instantiate descriptor classes at c=
lass-level is performance?

Performance might be part of it (it also saves some checks when
looking up attributes), but in my opinion a big reason for it is
separation of responsibilities. Classes define object behavior;
instances contain object state. For example, you can't define a method
on an instance (though you can certainly store a function there and
call it).