Henrik Faber <hfa...@invalid.net> wrote:
> Hi there,
>
> when I have a python class X which overloads an operator, I can use that
> operator to do any operation for example with an integer
>
> y = X() + 123
>
> however, say I want the "+" operator to be commutative. Then
>
> y = 123 + X()
>
> should have the same result. However, since it does not call __add__ on
> an instance of X, but on the int 123, this fails:
>
> TypeError: unsupported operand type(s) for +: 'int' and 'X'
>
> How can I make this commutative?
>
By defining __radd__
>>> class X:
def __add__(self, other):
return "%r + %r" % (self, other)
def __radd__(self, other):
return "%r + %r" % (other, self)
>>> X() + 123
'<__main__.X object at 0x029C45B0> + 123'
>>> 123 + X()
'123 + <__main__.X object at 0x02101910>'
--
Duncan Booth http://kupuguy.blogspot.com
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