[Python-Dev] Re: accumulator display syntax

Sat Oct 25 19:16:35 EDT 2003

> > No way. There's nothing that guarantees that a+=b has the same
> > semantics as a+b, and in fact for lists it doesn't.
>> You mean because += is more permissive (accepts any sequence
> RHS while + insists the RHS be specifically a list)? I don't see how
> this would make it bad to use += instead of + -- if we let the user
> sum up a mix of (e.g.) strings and tuples, why are we hurting him?

We specifically decided that sum() wasn't allowed for strings, because
it's a quadratic algorithm. Other sequences are just as bad, we just
didn't expect that to be a common case.
Also see my not-so-far-fetched example of a semantic change.
--Guido van Rossum (home page: http://www.python.org/~guido/)