Discover why 'if not mylist' is twice as fast as 'len(mylist) == 0' by examining CPython's VM instructions and object memory access patterns.
  • JasonDJ@lemmy.zipEnglish
    2·
    9 days ago

    if isinstance(mylist, list) and not mylist

    Problem solved.

    Or if not mylist # check if list is empty

    • gravitas_deficiency@sh.itjust.worksEnglish
      2·
      9 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.

      • JasonDJ@lemmy.zipEnglish
        0·
        9 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)

        • BlackRoseAmongThorns@slrpnk.netEnglish
          2·
          9 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.

        • gravitas_deficiency@sh.itjust.worksEnglish
          1·
          9 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.