this post was submitted on 12 Apr 2025
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195
Python Performance: Why 'if not list' is 2x Faster Than Using len() (blog.codingconfessions.com)
submitted 1 week ago by [email protected] to c/[email protected]
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[–] [email protected] 3 points 1 week ago (1 children)

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.

[–] [email protected] 1 points 1 week ago (2 children)

Ok, help a noob out. What is the difference between a sequence and an iterable? Is a sequence immutable, like a tuple?

[–] [email protected] 1 points 1 week ago (1 children)

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

[–] [email protected] 1 points 1 week ago

I know what an iterable is. But I am talking about Type[Iterable], which iirc does not obey falsey eval when empty.

[–] [email protected] 1 points 1 week ago* (last edited 1 week ago)

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)