int.__init__ incompatible in Python 3.3

Terry Reedy tjreedy at udel.edu
Thu Nov 8 21:29:38 CET 2012


On 11/8/2012 12:13 PM, Ian Kelly wrote:
> On Thu, Nov 8, 2012 at 8:55 AM, Ulrich Eckhardt
> <ulrich.eckhardt at dominolaser.com> wrote:

>> Preparing for an upgrade from 2.7 to 3, I stumbled across an incompatibility
>> between 2.7 and 3.2 on one hand and 3.3 on the other:
>>
>> class X(int):
>>      def __init__(self, value):
>>          super(X, self).__init__(value)

This is a bug. Subclasses of immutables should not define __init__.
 >>> int.__init__ is object.__init__
True

object.__init__(self) is a dummy placeholder function that takes no args 
and does nothing.

>> X(42)
>>
>> On 2.7 and 3.2, the above code works.

That is a bug. It is documented that calling with the wrong number of 
args is an error.

>> On 3.3, it gives me a "TypeError: object.__init__() takes no parameters".
 >> To some extent, this makes sense to
>> me, because the int subobject is not initialized in __init__ but in __new__.
>> As a workaround, I can simple drop the parameter from the call.

Just drop the do-nothing call.

>> breaking backward compatibility is another issue, so I wonder if that should
>> be considered as a bug.

Every bug fix breaks backward compatibility with code that depends on 
the bug. Such breakage is not a bug, but, as in this case, some fixes 
are not put in bugfix releases because of such breakage.

>> Bug? Feature? Other suggestions?

Intentional bugfix.
http://bugs.python.org/issue1683368
There was additional discussion on pydev or python-ideas lists before 
the final commit. This fix was not back-ported to 2.7 or 3.2.

> A similar change was made to object.__init__ in 2.6, so this could
> just be bringing the behavior of int into line with object.  There's
> nothing about it in the whatsnew document, though.

What's New is a summary of *new* features. It does not list bug fixes. 
At the top it says " For full details, see the Misc/NEWS file." The last 
patch on the issue added this entry.
'''
Core and Builtins
-----------------

- Issue #1683368: object.__new__ and object.__init__ raise a TypeError
if they are passed arguments and their complementary method is not 
overridden.
'''

> I say open a bug report and let the devs sort it out.

Please do not. The current situation is the result of 'sorting it out' 
over several years.


-- 
Terry Jan Reedy



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