[Python-Dev] binary operation heuristics -- bug or undocumented?

[Alex A. Naanou]

Thanks!

On Fri, Mar 19, 2010 at 16:05, Michael Foord <fuzzyman at voidspace.org.uk> wrote:
> On 19/03/2010 12:46, Alex A. Naanou wrote:
>>
>> [snip...]
>>>>>
>>>>> class C(object):
>>>>>
>>
>> ...     def __radd__(self, other):
>> ...         print 'C: adding C and %s objects.' % other.__class__.__name__
>> ...
>>
>>>>>
>>>>> a, b, c = A(), B(), C()
>>>>> 1 + c
>>>>>
>>
>> C: adding C and int objects.
>>
>>
>>
>
> That is the whole point of the __radd__ method. ints don't know how to add
> themselves to C objects, so int.__add__ will return NotImplemented and then
> Python will try C.__radd__.
>
> All the best,
>
> Michael
>
>> --uncut--
>>
>> My first expectation would be to get a TypeError here, as ints indeed
>> have an __add__ method, and they do not know anything about C objects
>> (obviously :) ). On second thought, giving client code priority to
>> handle things has it's merits.
>>
>> The problem is that I found no mention of this behavior in the docs.
>>
>>
>> P.S. tested in 2.5 through 3.0 and PyPy
>>
>> Thanks.
>>
>>
>
>
> --
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P.S. like the licence :)

>
>
>



-- 
Alex.