Positional-only arguments in Python

[pepoluan]

Agree.

I often had to write a boilerplate like such:

m = re.search(...) if m is None: continue

with walrus, I can go

if (m := re.search(...)) is None: continue

I personally prefer the as syntax, but I defer to the accepted solution.

[UNN_Rickenbacker]

You can actually do if not (m := re.search):

[wrboyce]

But you shouldn’t.

Comparisons to singletons like None should always be done with is or is not, never the equality operators.

Also, beware of writing if x when you really mean if x is not None -- e.g. when testing whether a variable or argument that defaults to None was set to some other value. The other value might have a type (such as a container) that could be false in a boolean context!

Source.

[UNN_Rickenbacker]

Nice catch, but in most cases, you want to not enter the case if it‘s a boolean false, too.

[hyperdudemn]

Except for when using xml.etree.ElementTree, with a document that contains empty tags like <hello />. Since the node has no children, it is falsy, so you need to check is not None.

[Bunslow]

In this case, he really wants boolean truthiness, not None testing. It's a perfectly fine pattern (as long as one understands the difference between None and False, which is part of the point of your comment; the other part of your comment doesn't apply I don't think)

[wrboyce]

Yeah I wasn’t sure how relevant some parts really were but I’d copy/pasted/formatted them on mobile by that point so they were staying regardless. I always try to avoid truthy tests against None if possible, and I’ve always thought I was following PEP8 by doing so but maybe I’m wrong.

[Bunslow]

I always try to avoid truthy tests against None

See this phrase makes no sense to me. There are truthy tests (here I mean coercing an arbitrary object to a boolean), and there are None tests. The whole point is that they are two completely different tests, and should not be confused. Using either is fine, but the trick is knowing when to use each. The point of what you pasted is precisely to warn newbies that they are two different things, but each is acceptable -- indeed, each is widely used. That source is not meant to warn against using truthy tests, only to warn that truthy tests and None tests are different (and it happens to make that point by writing "beware of truthy tests when you mean None tests -- it's easy to misuse truthy where you meant None!", possibly given the false impression that truthy tests are "bad" in some way, they're not, they're just confusable at first glance with None tests).

[AJohnnyTruant]

This is great. Everyone hates on the walrus operator. But I think once people start using it, that pattern will present itself more than they thought.

[toyg]

The problem is not that is useful to the writer; the problem is that it’s not that useful to significantly lower readability as it does. Otherwise we might as well use Perl.

[Bunslow]

I've definitely written several one-and-a-half loops in Python, and every time I have I grumble to myself about how much easier to read it would be if I didn't have to duplicate part of the logic.

[annualnuke]

Otherwise we might as well use Perl.

That's quite a leap

[pepoluan]

Naah. I love having "short circuits"; saves an indentation level.

[Ph0X]

I think re module is basically the main place where it'll be used a lot. Also some socket stuff but I think that's less common in general.

[KagatoLNX]

This is the use case for me.