[Python-Dev] [PEP] += on return of function call result

[Walter Dörwald]

Greg Ewing wrote:

> Andrew Koenig <ark@research.att.com>:
> 
> 
>>So the behavior of
>>
>>        foo = d.setdefault(r,'')
>>        foo += "test %d\n" % t
>>
>>depends on what type foo has, and the OP didn't say.
> 
> I assumed that the code snippet was from his actual application, in
> which case he *did* want it to work on strings, in which case, even if
> he had the feature he wanted, it wouldn't have helped him.
> [...]
> Being forced to find another way to update the value in this case is a
> feature, because the absence of such a way when the value is immutable
> makes it clear that there's no way to do what you're trying to do!

Mutable (or at least appendable) strings should probably be done with
StringIO/cStringIO. How about adding support for __iadd__ and
__str__ (and __unicode__) to both?

Bye,
    Walter Dörwald