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abhi9u@lemmy.world to Technology@lemmy.worldEnglish · 27 days ago

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

blog.codingconfessions.com

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

blog.codingconfessions.com

abhi9u@lemmy.world to Technology@lemmy.worldEnglish · 27 days ago
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Discover why 'if not mylist' is twice as fast as 'len(mylist) == 0' by examining CPython's VM instructions and object memory access patterns.
  • gravitas_deficiency@sh.itjust.works
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    26 days ago

    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.

    • JasonDJ@lemmy.zip
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      26 days ago

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

      • 48954246@lemmy.world
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        26 days ago

        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

        • gravitas_deficiency@sh.itjust.works
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          26 days ago

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

      • gravitas_deficiency@sh.itjust.works
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        26 days 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)

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