On 03/26/2018 04:18 AM, Steven D'Aprano wrote:
On Mon, Mar 26, 2018 at 11:14:43AM +0300, Kirill Balunov wrote:
Hi Chris, would you mind to add this syntactic form `(expr -> var)` to
alternative syntax section, with the same semantics as `(expr as var)`. It
seems to me that I've seen this form previously in some thread (can't find
where), but it does not appear in alt. syntax section.
That was probably my response to Nick:
https://mail.python.org/pipermail/python-ideas/2018-March/049472.html
I compared four possible choices:
target = default if (expression as name) is None else name
target = default if (name := expression) is None else name
target = default if (expression -> name) is None else name
target = default if (name <- expression) is None else name
The two arrow assignment operators <- and -> are both taken from R.
If we go down the sublocal scope path, which I'm not too keen on, then
Nick's earlier comments convince me that we should avoid "as". In that
case, my preferences are:
(best) -> := <- as (worst)
If we just bind to regular locals, then my preferences are:
(best) as -> := <- (worst)
Preferences are subject to change :-)
Obviously we're bikeshedding here, but personally I detest these kinds
of operators. To me - is a minus sign and < and > are less-than and
greater-than. Trying to re-use these characters in ways that depend on
their visual form strikes me as very ugly. <= makes sense because its
meaning is a combination of the *meanings* of < and =, but <- as
assignment is not a combination of the meanings of < and -. If we need
a two-character operator, I prefer something like := that doesn't try to
be a picture.
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