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Python Performance: Why 'if not list' is 2x Faster Than Using len()
(blog.codingconfessions.com)
this post was submitted on 12 Apr 2025
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As a Perl fossil I recognise this syntax as equivalent to
if(not @myarray)which does the same thing. And here I was thinking Guido had deliberately aimed to avoid Perlisms in Python.That said, the Perlism in question is the right* way to do it in Perl. The
lengthoperator does not do the expected thing on an array variable. (You get the length of the stringified length of the array. And a warning if those are enabled.)* You can start a fight with modern Perl hackers with whether
unless(@myarray)is better or just plain wrong, even if it works and is equivalent.Empty sequences being false goes back a lot further than perl, it was already a thing in the first lisp (in fact the empty list was the cannonical false).