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

borokov@lemmy.world ⁨1⁩ ⁨month⁩ ago

• dreugeworst@lemmy.ml ⁨1⁩ ⁨month⁩ ago

  why comment if you don’t even want to read the article? python lists are not linked lists, they’re contiguous with a smart growth strategy.

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  • sugar_in_your_tea@sh.itjust.works ⁨1⁩ ⁨month⁩ ago

    Like in most reasonable languages. Linked lists would be a terrible implementation for a list where grabbing arbitrary indices is explicitly supported.

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  • borokov@lemmy.world ⁨1⁩ ⁨month⁩ ago

    I comment because this is how a social network works, and this is how you keep lemmy alive. My comment has generated a dozen of other comments, so he achieved his goal.

    There is not a single question that’s already have been answered on internet, so there no point on asking anything on social plateforms except just for the sake of interacting with other peoples.

    Lemmy is not stackoverflow 😉

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    • dreugeworst@lemmy.ml ⁨1⁩ ⁨month⁩ ago

      If the point of Lemmy is just to generate as many comments as possible with everyone just assuming whatever they want about linked articles without reading them I’ll quickly leave again. I’m here for informed discussion, not for a competition in generating engagement

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• sugar_in_your_tea@sh.itjust.works ⁨1⁩ ⁨month⁩ ago

  Then please be less lazy next time.

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• riodoro1@lemmy.world ⁨1⁩ ⁨month⁩ ago

  So… it has to iterate over the whole empty list is what you’re saying? like once for every of the zero items in the lost?

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  • ChaoticNeutralCzech@feddit.org ⁨1⁩ ⁨month⁩ ago

    The list is not necessarily empty. If you were sure it was, why check?

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  • borokov@lemmy.world ⁨1⁩ ⁨month⁩ ago

    Don’t know how list are implemented in Python. But in the dumb linked list implementation (like C++ std::list), each element has a “next” member that point the the next element. So, to have list length, you have to do (pseudo code, not actual python code):

    len = 0
    elt = list.fisrt
    while exist(elt):
        elt = elt.next
        len++
    return len
    

    Whereas to test if list is empty, you just have to:

    return exist(list.first)
    

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    • riodoro1@lemmy.world ⁨1⁩ ⁨month⁩ ago

      That’s exactly what I was getting at. Getting length of an empty list would not even enter the loop.

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      • ChaoticNeutralCzech@feddit.org ⁨1⁩ ⁨month⁩ ago

        Yes. If it’s empty. But in cases where you need to check, it might as well not be.

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• Kacarott@aussie.zone ⁨1⁩ ⁨month⁩ ago

  No, len is a constant time operation, at least in most cases I believe.

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