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
      41·
      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.worksEnglish
        2·
        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.zipEnglish
          1·
          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.worksEnglish
            2·
            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.