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@abhi9u@lemmy.world to Technology@lemmy.worldEnglish • 1 year 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 • 1 year 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.
  • Sirber
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    0•1 year ago

    How does Python know of it’s my list or not?

    • @JasonDJ@lemmy.zip
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      0•1 year ago

      if isinstance(mylist, list) and not mylist

      Problem solved.

      Or if not mylist # check if list is empty

      • @gravitas_deficiency@sh.itjust.works
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        0•1 year ago

        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.

        • @JasonDJ@lemmy.zip
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          0•1 year ago

          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)

          • @gravitas_deficiency@sh.itjust.works
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            0•1 year 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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              0•1 year 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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                0•1 year 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

          • @BlackRoseAmongThorns@slrpnk.net
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            0•1 year ago

            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.

      • Sirber
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        0•1 year ago

        I think you missed the joke 😅

        • @PattyMcB@lemmy.world
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          0•1 year ago

          I thought it was funny!

    • dblsaiko
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      0•1 year ago

      Telemetry

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