__future__ and __rdiv__

[Ian Kelly]

On Sun, Jan 22, 2012 at 10:22 PM, Massimo Di Pierro <
massimo.dipierro at gmail.com> wrote:

> Hello everybody,
>
> I hope somebody could help me with this problem. If this is not the right
> place to ask, please direct me to the right place and apologies.
> I am using Python 2.7 and I am writing some code I want to work on 3.x as
> well. The problem can be reproduced with this code:
>
> # from __future__ import division
> class Number(object):
>    def __init__(self,number):
>        self.number=number
>    def __rdiv__(self,other):
>        return other/self.number
> print 10/Number(5)
>
> It prints 2 as I expect. But if I uncomment the first line, I get:
>
> Traceback (most recent call last):
>  File "test.py", line 8, in <module>
>    print 10/Number(5)
> TypeError: unsupported operand type(s) for /: 'int' and 'Number'
>
> Is this a bug or the __future__ division in 3.x changed the way operators
> are overloaded? Where can I read more?
>
>
In Python 3, the / operator uses __truediv__ and the // operator uses
__floordiv__.
In Python 2, the / operator uses __div__, unless the future import is in
effect, and then it uses __truediv__ like Python 3.

http://docs.python.org/reference/datamodel.html#emulating-numeric-types

Cheers,
Ian
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