> The sum function starts off with the integer 0, so it tries to add one
> of your objects to the integer 0.  This is probably what's going
> wrong.  You can pass as a second argument the thing you want sum to
> start with.  For example,

thanks ! much to my shame, i recall now that i was given this
explanation a long time ago, and forgot about it. In case anyone is
reading this: the quickest fix seems to add a __radd__(self,
wrongtype) method that just returns self. Works fine (kind of
dangerous sometimes of course...)

> You need to define the __repr__ method, since that is what list is
> using to display your objects.

ah. I try to avoid using __repr__ because i was told that this is
supposed to return a string from which the object can be reconstructed
-- and i certainly don't want to go through all that trouble just for
what i need. Do you know what happens if __repr__ simply returns the
same as __str__ ?

thanks again!
pierre
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