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Fri Oct 4 00:58:56 CEST 2013 · https://mail.python.org/pipermail/python-dev/2013-October/129155.html

Igor Vasilyev wrote:

> class A():
>     def __add__(self, var):
>         print("I'm in A class")
>         return 5
> a = A()
> a+1
> 1+a
> 
> Execution:
> python test.py
> I'm in A class
> Traceback (most recent call last):
>   File "../../test.py", line 7, in <module>
>     1+a
> TypeError: unsupported operand type(s) for +: 'int' and 'instance'

You need to define an __radd__ method for it to work
as a right-hand operand.

> When we adding class to integer we have both slotv and slotw. x = 
> slotv(v, w); -> returns Py_NotImplemented.
> But in this case we should execute x = slotw(v, w);

Yes, but the wrapper that gets put in the type slot calls
__rxxx__ instead of __xxx__ if it's being called for the
right-hand operand.

-- 
Greg

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[Python-Dev] summing integer and class