Comment

Comment on Python Performance: Why 'if not list' is 2x Faster Than Using len()

isn’t the expected behaviour exactly identical on any object that has len defined:

“By default, an object is considered true unless its class defines either a bool() method that returns False or a len() method that returns zero, when called with the object.”

source

Sort:hotnew top

CompassRed@discuss.tchncs.de ⁨6⁩ ⁨days⁩ ago
It’s not the same, and you kinda answered your own question with that quote. Consider what happens when an object defines both dunder bool and dunder len. It’s possible for dunder len to return 0 while dunder bool returns True, in which case the falsy-ness of the instance would not depend at all on the value of len

source
thebestaquaman@lemmy.world ⁨6⁩ ⁨days⁩ ago
Exactly as you said yourself: Checking falsieness does not guarantee that the object has a length. There is considerable overlap between the two, and if it turns out that this check is a performance bottleneck (which I have a hard time imagining) it can be appropriate to check for falsieness instead of zero length. But in that case, don’t be surprised if you suddenly get an obscure bug because of some custom object not behaving the way you assumed it would.

I guess my primary point is that we should be checking for what we actually care about, because that makes intent clear and reduces the chance for obscure bugs.

source