[Python-Dev] Semantics of __int__(), __index__()

Ethan Furman ethan at stoneleaf.us
Wed Apr 3 19:50:21 CEST 2013

On 04/03/2013 10:46 AM, Barry Warsaw wrote:
> On Apr 04, 2013, at 03:04 AM, Steven D'Aprano wrote:
>> On 04/04/13 01:16, Barry Warsaw wrote:
>>> the other built-in types-as-functions, so int() calls __int__() which must
>>> return a concrete integer.
>> Why must it? I think that's the claim which must be justified, not just taken
>> as a given.  When we call n = int(something), what's the use-case for caring
>> that n is an instance of built-in int but not of a subclass, and is that
>> use-case so compelling that it must be enforced for all uses of int() etc.?
> It's a consistency-of-implementation issue.  Where built-in types are
> callable, they return concrete instances of themselves.  This is true for
> e.g. list, tuple, dict, bytes, str, and should also be true of int.


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