Comment on Python Performance: Why 'if not list' is 2x Faster Than Using len()

if (foo is not None) and not foo:
   ...

if (foo is not None) and (len(foo) == 0):
  ...

• gigachad@sh.itjust.works ⁨6⁩ ⁨days⁩ ago

  This is what I would come up with:

  try:
      if len(foo) == 0:
      ...
  except TypeError:
      ...
  

  There is no need to add a None check, as foo being None should be considered as a faulty input. Avoiding the possibility of foo being None from the beginning using static checks or testing is of course the preferred solution. But in reality we do not work in such optimal environments, at least I can say that from the perspective of data science, where often procedural, untested code is produced that runs only a few times. But I get your point and I think both paths are viable, maybe we can agree on that :)

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  • sugar_in_your_tea@sh.itjust.works ⁨6⁩ ⁨days⁩ ago

    That’s terrible, and I would block that PR in a heartbeat, unless there was a very good reason for it (given context). I would instead prefer:

    if foo is None:
        ...
    

    Exceptions are useful for bubbling up errors, they’re a massive code smell if you’re catching something thrown by local logic. Just like you shouldn’t catch IndexError right after indexing a list, you shouldn’t catch TypeError right after checking the length. If you need to check parameters, check them at the start of your function and return early.

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    • gigachad@sh.itjust.works ⁨6⁩ ⁨days⁩ ago

      Sir, I will make sure to never bother you with a PR and my terrible, terrible code ;)

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      • sugar_in_your_tea@sh.itjust.works ⁨6⁩ ⁨days⁩ ago

        Rejecting a PR shouldn’t be offensive, it should be a learning opportunity, both for the reviewer and the submitter. If I reject it, I’ll give a clear reason why, and suggestions on how to fix it.

        So please bother me with terrible, terrible code. I want to take time out of my day to help contributors learn, and I like pointing out areas where I learn something as well (like, “hey, this is really clever and also really easy to read, good job!”). I’m not always right, but I do have a lot of experience that I think others could benefit from. I know I was deeply appreciative of constructive criticism as a new dev, and I hope that’s true for the people I provide reviews for.

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