Comment on Python Performance: Why 'if not list' is 2x Faster Than Using len()
sugar_in_your_tea@sh.itjust.works 2 days agoWell yeah, because I’m explicitly not defining a difference between None and []. In most cases, the difference doesn’t matter.
If I did want to differentiate, I’d use another if block:
if foo is None: ... if not foo: ...
Explicit is better than implicit. I hate relying on exceptions like len(foo) == 0 raising a TypeError because that’s very much not explicit.
Exceptions should be for exceptional cases, as in, things that aren’t expected. If it is expected, make an explicit check for it.
LegoBrickOnFire@lemmy.world 2 days ago
I don’t really understand the point about exceptions. Yeah “not foo” cannot throw an exception. But the program should crash if an invalid input is provided. If the function expects an optional[list] it should be provided with either a list or None, nothing else.
sugar_in_your_tea@sh.itjust.works 2 days ago
Sure. But is
Noneinvalid input in your case, whereas[]is valid? If so, make that check explicit, don’t rely on an implicit check thatlen(…)does.When I see
TypeErrorin the logs, I assume the developer screwed up. When I seeValueErrorin the logs, I assume the user screwed up. Ideally,TypeErrorshould never happen, and every case where it could happen should transform it to another type of exception that indicates where the error actually lies.The only exceptions I want to see in my code are:
Implicit ones like accessing attributes on
Noneor calling methods that don’t exist shouldn’t be happening in production code.LegoBrickOnFire@lemmy.world 2 days ago
I agree. So if None is a valid input we should check it first, and then check if the length is zero. In this situation, we see a type error only if the programmer screwed up and everything is explicit
sugar_in_your_tea@sh.itjust.works 2 days ago
Yes. If
Noneis just as valid and has the same meaning as[]for the function (true more often than not), just doif not foo. IfNoneshould be handled separately from[]for some reason, treat them both separately so it’s absolutely clear.And I especially like this one:
The one obvious way to check if you have data is
if foo. That works for pretty much everything as you’d expect. Explicitly deviating from that is a cue to the reader that they should pay attention. In this case, that meansNoneis semantically different than empty data, and that’s something the reader should be aware of.