On 9 Oct 2023, at 08:58, Stephen J. Turnbull
<turnbull.stephen...@u.tsukuba.ac.jp> wrote:
> ...
> Not sure what you're getting at here, that's an infloop. Did you mean
> something like this:
>
> class A:
> def func(self):
> while (self.a := self.a += 1) < 5:
> pass
> return self.a
Mistake, late night. I just meant to portray initialisation via walrus inside
statement, nothing more. It doesn’t work with while loop. The intention was
this, which is also principal use-case from previous reply:
class A:
def func(self, string):
if self.a := re.match('.*', string):
print(self.a)
return self.a.group()
Generally, this would be useful for all examples of
https://peps.python.org/pep-0572/ <https://peps.python.org/pep-0572/>
, where “initial” value is an attribute or dictionary item.
>> Same argument as for “walrus” operator itself - convenient
>> feature. Or is there more to it?
>
> There's more to it. The loop and a half construct, where you execute
> the body of the loop once outside the loop for some reason is widely
> considered a really big wart (DRY failure). The walrus allows us to
> eliminate most of those.
>
> On the other hand, an assignment and a return statement are two
> different things; it's not a DRY viotion to have the same identifier
> in both.
I see. Could you give an example of this? I vaguely remember this sometimes
being the case, but can not find anything now on this in relation to walrus
operator. Is there no way to bring that execution within the body without
walrus operator?
>> I was actually surprised that this didn’t work - I thought that
>> this operator is a literal composite of assignment and “retriever",
>> rather than having it’s own restrictive logic.
>
> This is a common practice in Python development. Try a little bit of
> a new idea, avoid engineering, and expand later if that seems useful
> too.
Fair.
>> If it doesn’t break anything, doesn’t have any undesirable side
>> effects and community likes it, then could be a good addition.
>
> "Community likes it" is a null predicate, very hard to verify in edge
> cases. When the support in the community is strong enough that
> "community likes it" is common knowledge, it's always the case that
> there are objective reasons why it's a good thing.
>
> All additions have a 0 * infinity cost: a negligible cost of learning
> (for one user) times *all* the users.
Ok, thanks.
DG
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