Class Variable Access and Assignment

Antoon Pardon apardon at forel.vub.ac.be
Fri Nov 4 09:08:42 CET 2005


Op 2005-11-03, Steven D'Aprano schreef <steve at REMOVETHIScyber.com.au>:
> On Thu, 03 Nov 2005 04:30:09 -0800, Paul Rubin wrote:
>
>> Steve Holden <steve at holdenweb.com> writes:
>>> > class A:
>>> >   a = 1
>>> > b = A()
>>> > b.a += 2
>>> > print b.a
>>> > print A.a
>>> > Which results in
>>> > 3
>>> > 1
>>> >
>>> I don't suppose you'd care to enlighten us on what you'd regard as the
>>> superior outcome?
>> 
>>     class A:
>>       a = []
>>     b = A()
>>     b.append(3)
>>     print b.a
>>     print a.a
>> 
>> Compare and contrast.
>
>
> I take it then that you believe that ints like 1 should be mutable like
> lists? Because that is what the suggested behaviour implies.

No it isn't.

One other way, to implement the += and likewise operators would be
something like the following.

Assume a getnsattr, which would work like getattr, but would also
return the namespace where the name was found. The implementation
of b.a += 2 could then be something like:

  ns, t = getnsattr(b, 'a')
  t = t + 2
  setattr(ns, 'a')


I'm not arguing that this is how it should be implemented. Just
showing the implication doesn't follow.

-- 
Antoon Pardon



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