[Python-Dev] Semantics of __int__(), __index__()
stefan_ml at behnel.de
Fri Apr 5 08:22:12 CEST 2013
Guido van Rossum, 04.04.2013 23:14:
> On Thu, Apr 4, 2013 at 1:50 PM, Tim Delaney wrote:
>> I fall into:
>> 1. int(), float(), str() etc should return that exact class (and
>> operator.index() should return exactly an int).
>> 2. It could sometimes be useful for __int__() and __index__() to return a
>> subclass of int.
>> So, for the int constructor, I would have the following logic (assume
>> appropriate try/catch):
>> def __new__(cls, obj):
>> i = obj.__int__()
>> if type(i) is int:
>> return i
>> return i._internal_value
> CPython can solve this in C using an unsafe cast, and the code that
> checks for allowable subclasses of int actually ensures such a cast
> will work. But it still feels wrong; __int__ should be expected to do
> the work.
+1, that's why it's called "__int__" (even if it returns a PyLong in Py3 ;)
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