sum() requires number, not simply __add__

Arnaud Delobelle arnodel at
Thu Feb 23 16:32:43 EST 2012

On 23 February 2012 21:19, Buck Golemon <buck at> wrote:
> I feel like the design of sum() is inconsistent with other language
> features of python. Often python doesn't require a specific type, only
> that the type implement certain methods.
> Given a class that implements __add__ why should sum() not be able to
> operate on that class?

It can.  You need to pass a second argument which will be the start
value.  Try help(sum) for details.


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