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Python Performance: Why 'if not list' is 2x Faster Than Using len()
(blog.codingconfessions.com)
this post was submitted on 12 Apr 2025
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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?
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)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.
https://docs.python.org/3/library/collections.abc.html#collections-abstract-base-classes
I know what an iterable is. But I am talking about
Type[Iterable], which iirc does not obey falsey eval when empty.Not really, generators have weird truthiness, i don't remember if they evaluate to true or false, but they cannot be checked for emptiness so they default to either always true or always false.