abhi9uPython Performance: Why 'if not list' is 2x Faster Than Using len()
SirberHow does Python know of it’s my list or not?
if isinstance(mylist, list) and not mylist
Problem solved.
Or if not mylist # check if list is empty
You’re checking if
mylist is falsey. Sometimes that’s the same as checking if it’s empty, if it’s actually a list, but that’s not guaranteed.
Doesn’t Python treat all empty iterables as false tho? This isn’t unique to python, is it? (though I’m not a programmer…just a dude who writes scripts every now and then)
My point is that the second statement you presented can have the effect of evaluating emptiness of a Sequence (note: distinct from an Iterable), but that only holds true if the target of the conditional IS a sequence. I’m underlining the semantic difference that was elided as a result of falsey evaluation.
Ok, help a noob out. What is the difference between a sequence and an iterable? Is a sequence immutable, like a tuple?
An iterable is just something that can be iterated over, like range(10), or [1, 2, 3].
A sequence on the other hand is a Collection that is reversible.
I know what an iterable is. But I am talking about
Type[Iterable], which iirc does not obey falsey eval when empty.
thing: Sequence[Any] iirc is iterable, indexable, and reversible.
thing: Iterable[Any] only guarantees that its iterable - and note that iterating can sometimes have the effect of consuming the iterable (e.g. when working with streaming interfaces)