Tim Peters <[EMAIL PROTECTED]> wrote:
>
> Anyone remember why setdefault's second argument is optional?
>
> >>> d = {}
> >>> d.setdefault(666)
> >>> d
> {666: None}
For quick reference for other people, d.setdefault(key [, value])
returns the value that is currently there, or just assigned. The only
case where it makes sense to omit the value parameter is in the case
where value=None.
> just doesn't seem useful. In fact, it's so silly that someone calling
> setdefault with just one arg seems far more likely to have a bug in
> their code than to get an outcome they actually wanted. Haven't found
> any 1-arg uses of setdefault() either, except for test code verifying
> that you _can_ omit the second arg.
>
> This came up in ZODB-land, where someone volunteered to add
> setdefault() to BTrees. Some flavors of BTrees are specialized to
> hold integer or float values, and then setting None as a value is
> impossible. I resolved it there by making BTree.setdefault() require
> both arguments. It was a surprise to me that dict.setdefault() didn't
> also require both.
>
> If there isn't a sane use case for leaving the second argument out,
> I'd like to drop the possibility in P3K (assuming setdefault()
> survives).
I agree, at least that in the case where people actually want None (the
only time where the second argument is really optional, I think that
they should have to specify it. EIBTI and all that.
- Josiah
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