Python 3.1, object, and setattr()

[Steve Howell]

On Apr 1, 6:46 am, Ethan Furman <et... at stoneleaf.us> wrote:
> Greetings!
>
> Perhaps I woke up too early this morning, but this behaviour has me baffled:
>
> Python 3.1.1 (r311:74483, Aug 17 2009, 17:02:12) [MSC v.1500 32 bit
> (Intel)] on win32
> Type "help", "copyright", "credits" or "license" for more information.
>
> --> test = object()
>
> --> setattr(test, 'example', 123)
> Traceback (most recent call last):
>    File "<stdin>", line 1, in <module>
> AttributeError: 'object' object has no attribute 'example'
>
> Shouldn't setattr() be creating the 'example' attribute?  Any tips
> greatly appreciated!
>

On 2.6.2 the error seems to be limited to instances of object.  If you
subclass object, you are fine.  I do not know why that is so; I'm just
verifying that the behavior you see is not limited to 3.1.1.

 Python 2.6.2 (release26-maint, Apr 19 2009, 01:56:41)
 [GCC 4.3.3] on linux2
 Type "help", "copyright", "credits" or "license" for more
information.
 >>> class Foo(object): pass
 ...
 >>> test = Foo()
 >>> setattr(test, 'example', 123)
 >>> test.example
 123
 >>> test = object()
 >>> setattr(test, 'example', 123)
 Traceback (most recent call last):
   File "<stdin>", line 1, in <module>
 AttributeError: 'object' object has no attribute 'example'

It's probably good to subclass object anyway, with something like:

  class Record(object):
      pass

But I do not know your use case.