Re: Commutative object in emulating numbers

[Steven D'Aprano]

On Sun, 13 Sep 2009 21:52:26 -0700, iu2 wrote:

> Hi,
> 
> I reached the chapter "Emulating numeric types" in the python
> documentation and I tried this:
[...]
> What do I need to do in order to make the two classes, int and A,
> commutative?


Try adding a __rmul__ method:


class A:
def __mul__(self, a):
return 'A' * a
__rmul__ = __mul__



-- 
Steven
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Re: Commutative object in emulating numbers

[iu2]

On Sep 14, 8:16 am, Chris Rebert  wrote:
> On Sun, Sep 13, 2009 at 9:52 PM, iu2  wrote:
> > Hi,
>
> > I reached the chapter "Emulating numeric types" in the python
> > documentation and I tried this:
>
>  class A:
> >        def __mul__(self, a):
> >                return 'A' * a
>
> > Now, this works as expected:
>  a = A()
>  a * 3
> > 'AAA'
>
> > But this doesn't (also as expected):
>  3 * a
>
> > Traceback (most recent call last):
> >  File "", line 1, in 
> >    3 * a
> > TypeError: unsupported operand type(s) for *: 'int' and 'instance'
>
> > What do I need to do in order to make the two classes, int and A,
> > commutative?
>
> You need to define 
> __rmul__():http://docs.python.org/dev/3.0/reference/datamodel.html#object.__rmul__
>
> Cheers,
> Chris
> --http://blog.rebertia.com- Hide quoted text -
>
> - Show quoted text -

Thanks!
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Re: Commutative object in emulating numbers

[Chris Rebert]

On Sun, Sep 13, 2009 at 9:52 PM, iu2  wrote:
> Hi,
>
> I reached the chapter "Emulating numeric types" in the python
> documentation and I tried this:
>
 class A:
>        def __mul__(self, a):
>                return 'A' * a
>
> Now, this works as expected:
 a = A()
 a * 3
> 'AAA'
>
> But this doesn't (also as expected):
 3 * a
>
> Traceback (most recent call last):
>  File "", line 1, in 
>    3 * a
> TypeError: unsupported operand type(s) for *: 'int' and 'instance'

>
> What do I need to do in order to make the two classes, int and A,
> commutative?

You need to define __rmul__():
http://docs.python.org/dev/3.0/reference/datamodel.html#object.__rmul__

Cheers,
Chris
--
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Re: Commutative object in emulating numbers

[iu2]

On Sep 14, 7:52 am, iu2  wrote:
> Hi,
>
> I reached the chapter "Emulating numeric types" in the python
> documentation and I tried this:
>
> >>> class A:
>
>         def __mul__(self, a):
>                 return 'A' * a
>
> Now, this works as expected:>>> a = A()
> >>> a * 3
>
> 'AAA'
>
> But this doesn't (also as expected):
>
> >>> 3 * a
>
> Traceback (most recent call last):
>   File "", line 1, in 
>     3 * a
> TypeError: unsupported operand type(s) for *: 'int' and 'instance'
>
>
>
> What do I need to do in order to make the two classes, int and A,
> commutative?
> (In the same way that string and int are commutative over "*")
> Thanks

By commutative I mean give the same result, that is
3 * a
will also return 'AAA'
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Commutative object in emulating numbers

[iu2]

Hi,

I reached the chapter "Emulating numeric types" in the python
documentation and I tried this:

>>> class A:
def __mul__(self, a):
return 'A' * a

Now, this works as expected:
>>> a = A()
>>> a * 3
'AAA'

But this doesn't (also as expected):
>>> 3 * a

Traceback (most recent call last):
  File "", line 1, in 
3 * a
TypeError: unsupported operand type(s) for *: 'int' and 'instance'
>>>

What do I need to do in order to make the two classes, int and A,
commutative?
(In the same way that string and int are commutative over "*")
Thanks
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