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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 Thu, 19 Dec 2013 00:45:02 +1300
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Ethan Furman wrote:
>> This leads to another question: we've now seen two examples where
>> (presumably) the internal type field and __class__ differ. In the
>> weakproxy case, type(obj) returns the internal type field. In the
>> "regular" case, where you set obj.__class__ to a class, type(obj) returns
>> the new (external) type. How the hell does it decide which one to return?

When you set the __class__ of a regular object and it
succeeds, it actually changes the internal type, i.e.
obj->ob_type at the C level.

This is only allowed under certain conditions. Mostly
only for user-defined classes, and only if the layouts
of the old and new instance structs are compatible.

-- 
Greg

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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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