this post was submitted on 12 Apr 2025
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195
Python Performance: Why 'if not list' is 2x Faster Than Using len() (blog.codingconfessions.com)
submitted 1 week ago by [email protected] to c/[email protected]
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[–] [email protected] 2 points 1 week ago (1 children)

Apart from the quote from the zen of python, does this really make your code better though? You will end up writing 4-5 lines with an extra level of indentation. The code does the same, but has worse performance and communicates the intent poorly (compared to the “pythonic” version).

[–] [email protected] 1 points 1 week ago (1 children)

I am not saying it's better, just that I don't like the proposed way :) I would argue that being "pythonic" has even less value than the Zen, which I quoted because it's true, not because it is some strict rule (which it isn't anyway).

You could argue I also need to write that extra code for the if not case, as I explicitly have to check if it is None if my program somewhere further down expects only lists.

Hunting for those sweet milliseconds is a popular game in the Python community ;) if this mechanism is that important for your program, you should definitely use it, I would do as well!

[–] [email protected] 2 points 1 week ago (1 children)

I think pythonic is more important than performance and I would still choose that version over a try-catch block, were it slower. Being pythonic means it represents a commonly understood pattern in Python code, therefore it is more efficient in communicating intent.

[–] [email protected] 2 points 1 week ago

Exactly. The point of following a code style is to make obvious patterns easy to spot and deviations stand out. That's why code style guidelines say your priorities should be:

  1. follow whatever style the code around it uses
  2. follow project style guidelines
  3. do the technically optimal option

3 should only be prioritized if the win is big enough, and there should probably be a comment right there explaining why the deviation was made.