On Sunday 26 October 2003 04:41 pm, Phillip J. Eby wrote:
At 04:16 PM 10/25/03 -0700, Guido van Rossum wrote:
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. ... assumed that he meant he would change it so that the *first* addition would use + (in order to ensure getting a "fresh" object) and then subsequent additions would use +=.
A better architecture than the initial copy.copy I was now thinking of -- thanks. But it doesn't solve Guido's objection as above shown.
If this were the approach taken, it seems to me that there could not be any semantic change or side-effects for types that have compatible meaning for + and += (i.e. += is an in-place version of +).
Maybe I'm missing something here?
Only the fact that "there's nothing that guarantees" this, as Guido says. alist = alist + x only succeds if x is also a list, while alist += x succeeds also for tuples and other sequences, for example. Personally, I don't think this would be a problem, but it's not my decision. Alex