195
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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Could also compare against:
That way this version isn’t evaluating two functions. The bool evaluation of an integer is false when zero, otherwise true.
This is honestly the worst version regarding readability. Don't rely on implicit coercion, people.
But the first example does the same thing for an empty list. I guess the lesson is that if you’re measuring the speed of arbitrary stylistic syntax choices, maybe Python isn’t the best language for you.
Yes, the first example does the same thing, but there's still less to mentally parse. Ideally you should just use
if len(mylist) == 0:.That's worse. IMO, solve this problem with two things:
mylistaslist | Noneor justlistif not mylist:The first documents intent and gives you static analysis tools some context to check for type consistency/compatibility, and the second shows that
Nonevs empty isn't an important distinction here.