I just want to note that this is just a gentle suggestion/observation, in case
this wasn’t done yet.
I am not pushing this.
——
All good points, thank you.
——
Why would this not be a good option? 1 extra line compared to walrus, but no
DRY issue.
with open(“fn") as f:
while True:
line = f.readline()
if line and check(line):
process(line)
else:
break
DG
> On 9 Oct 2023, at 15:52, Stephen J. Turnbull
> <[email protected]> wrote:
>
> Dom Grigonis writes:
>
>> Mistake, late night. I just meant to portray initialisation via
>> walrus inside statement, nothing more. It doesn’t work with while
>> loop.
>
> It *does* work with a while loop, just not that one. See below. The
> problem is that you're writing new code full of trash you don't need
> to explain the concept. Keep these examples as simple as possible.
> For example, my "pass" example is too simple if you want to show how
> the walrus can save typing because it doesn't save any lines of code;
> you need something a little more complicated to demonstrate that
> saving.
>
> In the progress of any proposal to acceptance, at some point someone
> is going to say, "I see that it works and solves a theoretical
> problem, but who would ever use it?" At that point you go into a
> large body of code such as the Python standard library or numpy to
> find realistic examples. But that's old code, and only needed to
> demonstrate actual utility.
>
>> 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.
>
> That's not the question though. The question is are those examples
> themselves frequently useful. And that's when you go find them in the
> stdlib.
>
>> 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?
>
> The problem is code like this:
>
> with open("a_file") as f:
> while (line := f.readline())
> if check(line):
> process(line)
> else:
> break
>
> There is no way to do that without an assignment, and without the
> walrus you need an assignment before the while, and the same
> assignment within the loop body. Is that a big deal? No. In fact, I
> have never used the walrus operator in anger, nor wanted to. I'm just
> as happy to write
>
> with open("a_file") as f:
> line = f.readline()
> while (line)
> if check(line):
> process(line)
> else:
> break
> line = f.readline()
>
> But some people find loop-and-a-half extremely ugly, and while I
> differ on "extremely", I can't deny that it's ugly.
>
> You *could* do this for small files with
>
> with open("a_file") as f:
> lines = f.readlines()
> for (line in lines):
> if check(line):
> process(line)
> else:
> break
>
> but that's not possible with an infinite iterable, undesireable for
> most non-file streams, etc.
>
> Re "simple examples", see why I used the "if check()" stuff? If I
> wasn't going to talk about infinite iterables and pausing external
> streams, that would just be (potentially wrong!) complexity that
> doesn't help explain anything.
>
> Steve
>
>
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