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

sirber@lemmy.ca ⁨3⁩ ⁨days⁩ ago

• 2xsaiko@discuss.tchncs.de ⁨3⁩ ⁨days⁩ ago

  Telemetry

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• JasonDJ@lemmy.zip ⁨3⁩ ⁨days⁩ ago

  if isinstance(mylist, list) and not mylist

  Problem solved.

  Or if not mylist # check if list is empty

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  • sirber@lemmy.ca ⁨2⁩ ⁨days⁩ ago

    I think you missed the joke 😅

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    • PattyMcB@lemmy.world ⁨2⁩ ⁨days⁩ ago

      I thought it was funny!

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  • gravitas_deficiency@sh.itjust.works ⁨3⁩ ⁨days⁩ 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.

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    • JasonDJ@lemmy.zip ⁨2⁩ ⁨days⁩ 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)

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      • gravitas_deficiency@sh.itjust.works ⁨2⁩ ⁨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.

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      • BlackRoseAmongThorns@slrpnk.net ⁨2⁩ ⁨days⁩ 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.

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• jj4211@lemmy.world ⁨1⁩ ⁨day⁩ ago

  else: # not my list, it is ourlist

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• gargolito@lemm.ee ⁨2⁩ ⁨days⁩ ago

  Python likes giving lists.

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