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Re: Basic misunderstanding on object creation

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On 5/13/2015 9:25 AM, andrew cooke wrote:

> The following code worked on Python 3.2, but no longer works in 3.4.

Bugfixes break code that depends on buggy behavior. See
https://bugs.python.org/issue1683368
Your code also fails in 2.7.9 if you inherit Foo from object.
The exact error messages changed for 3.4 in
https://bugs.python.org/issue7963

 > Did something change,

Obviously yes.

 > or have I always been doing something dumb?

You were depending on behavior of object that Guido decided was buggy.

I found the tracker issue by looking for 'object' in the Core and 
Builtins sections of the changelog one can access from What's New, first 
paragraph (using Highlight All in Firefox).

>>>> class Foo:
> ...     def __new__(cls, *args, **kargs):
> ...         print('new', args, kargs)
> ...         super().__new__(cls, *args, **kargs)
> ...
>>>> class Bar(Foo):
> ...     def __init__(self, a):
> ...         print('init', a)
> ...
>>>> Bar(1)
> new (1,) {}
> Traceback (most recent call last):
>    File "<stdin>", line 1, in <module>
>    File "<stdin>", line 4, in __new__
> TypeError: object() takes no parameters
>
> What I was expecting to happen (and what happens in 3.2) is that the object.__new__ method passes the argument to the __init__ of the subclass.

-- 
Terry Jan Reedy

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Thread

Basic misunderstanding on object creation andrew cooke <andrew@acooke.org> - 2015-05-13 06:25 -0700
  Re: Basic misunderstanding on object creation Thomas Rachel <nutznetz-0c1b6768-bfa9-48d5-a470-7603bd3aa915@spamschutz.glglgl.de> - 2015-05-13 16:24 +0200
    Re: Basic misunderstanding on object creation andrew cooke <andrew@acooke.org> - 2015-05-13 07:42 -0700
      Re: Basic misunderstanding on object creation andrew cooke <andrew@acooke.org> - 2015-05-13 07:45 -0700
        Re: Basic misunderstanding on object creation Peter Otten <__peter__@web.de> - 2015-05-13 16:55 +0200
        Re: Basic misunderstanding on object creation Ian Kelly <ian.g.kelly@gmail.com> - 2015-05-13 08:55 -0600
          Re: Basic misunderstanding on object creation andrew cooke <andrew@acooke.org> - 2015-05-13 08:52 -0700
      Re: Basic misunderstanding on object creation Ian Kelly <ian.g.kelly@gmail.com> - 2015-05-13 08:54 -0600
  Re: Basic misunderstanding on object creation Terry Reedy <tjreedy@udel.edu> - 2015-05-13 12:36 -0400
    Re: Basic misunderstanding on object creation andrew cooke <andrew@acooke.org> - 2015-05-13 11:42 -0700
      Re: Basic misunderstanding on object creation Terry Reedy <tjreedy@udel.edu> - 2015-05-13 15:17 -0400
      Re: Basic misunderstanding on object creation Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-05-13 20:45 +0100
        Re: Basic misunderstanding on object creation Ned Batchelder <ned@nedbatchelder.com> - 2015-05-13 13:33 -0700
          Re: Basic misunderstanding on object creation Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-05-14 11:07 +1000
  Re: Basic misunderstanding on object creation Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-05-13 17:38 +0100
  Re: Basic misunderstanding on object creation Terry Reedy <tjreedy@udel.edu> - 2015-05-13 13:05 -0400
  Re: Basic misunderstanding on object creation Terry Reedy <tjreedy@udel.edu> - 2015-05-13 13:13 -0400
  Re: Basic misunderstanding on object creation Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-05-13 18:43 +0100

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