Re: Type of an object:

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From	Gregory Ewing <greg.ewing@canterbury.ac.nz>
Newsgroups	comp.lang.python
Subject	Re: Type of an object:
Date	Wed, 18 Dec 2013 11:15:03 +1300
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Steven D'Aprano wrote:
> Well, that is a surprise, but I don't think that is intended behaviour. I 
> think that's something which only works by accident. The intention is 
> that __class__ returns the instance's type, not arbitrary values.

Well, a proxy object would obviously return a suitable
class-like object. I was just demonstrating that it's
possible to override what __class__ returns.

I don't think it's an accident, because the weakref
module uses this for its proxy objects.

 >>> import weakref
 >>> class C(object):
...  pass
...
 >>> c = C()
 >>> p = weakref.proxy(c)
 >>> p.__class__
<class '__main__.C'>
 >>> type(p)
<type 'weakproxy'>

> If you 
> try to set it to a non-class on the instance, it fails:

For proxying purposes you don't need to be able to set
it, but I don't see why you couldn't use a property
setter to override that behaviour as well if you really
wanted to.

-- 
Greg

Thread

Type of an object: ‘obj.__class__’ versus ‘type(obj)’ Ben Finney <ben+python@benfinney.id.au> - 2013-12-16 12:51 +1100
  Re: Type of an object: ‘obj.__class__’ versus ‘type(obj)’ Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-12-16 22:17 +0000
    Re: Type of an object: ‘obj.__class__’ versus ‘type(obj)’ dieter <dieter@handshake.de> - 2013-12-17 08:14 +0100
      Re: Type of an object: ‘obj.__class__’ versus ‘type(obj)’ Steven D'Aprano <steve@pearwood.info> - 2013-12-17 07:42 +0000
        Re: Type of an object: Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2013-12-17 23:35 +1300
          Re: Type of an object: Ethan Furman <ethan@stoneleaf.us> - 2013-12-17 06:50 -0800
          Re: Type of an object: Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-12-17 15:08 +0000
            Re: Type of an object: Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2013-12-18 11:15 +1300
              Re: Type of an object: Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-12-17 23:51 +0000
                Re: Type of an object: Ethan Furman <ethan@stoneleaf.us> - 2013-12-17 17:10 -0800
                Re: Type of an object: Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2013-12-19 00:45 +1300
                Re: Type of an object: Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2013-12-19 00:39 +1300

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