Szabolcs <[EMAIL PROTECTED]> wrote:
> On May 5, 9:37 am, Szabolcs Horvát <[EMAIL PROTECTED]> wrote:
>> Gabriel Genellina wrote:
>>
>> > Python doesn't require __add__ to be associative, so this should
>> > not be
> used as a general sum replacement.
>>
>> It does not _require_ this, but using an __add__ that is not
>> commutative and associative, or has side effects, would qualify as a
>> serious misuse, anyway.
>
> Sorry, I meant associative only, not commutative.
>
Unfortunately an __add__ which is not associative is actually perfectly
reasonable. For example you could have a Tree class where adding two trees
returns a new tree so (a+b)+c gives you:
.
/ \
. c
/ \
a b
but a+(b+c) gives:
.
/ \
a .
/ \
b c
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