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A comment on WTF Python: Exploring and understanding Python through surprising snippets. Parent comment

Re:WTF Python: Exploring and understanding Python through su... by shoo on Thursday February 11, 2021 @03:52AM (#26099568)
I agree about explicit None checks. It is often useful to distinguish None from the zero value of a type such as a numeric zero, empty string or empty collection. I also write "is None" & "is not None" everywhere when doing these explicit checks.

Yet the same be benefits of explicit None checks can be attained by writing "== None" i.e. doing value based comparisons against a None value. So this argument does not explain why "is" is necessary.

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Re:WTF Python: Exploring and understanding Python through su... by pansa2 on Thursday February 11, 2021 @03:56AM (#26099591)
I think the reason not to write `== None` is that classes can override `==`:

    class C:
        def __eq__(self, other): return True
    C() == None  # True
    C() is None  # False
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Re:WTF Python: Exploring and understanding Python through su... by eirki on Thursday February 11, 2021 @06:13AM (#26100315)
It is also marginally faster, I think.
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Re:WTF Python: Exploring and understanding Python through su... by dagw on Thursday February 11, 2021 @09:50AM (#26101992)
Just did a quick check, and looping over an array of 1 million Nones and checking each element

  el==None
was roughly 25% slower than

  el is None
edit: Doing

  None==el
was roughly 15% slower
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Re:WTF Python: Exploring and understanding Python through su... by dragonwriter on Thursday February 11, 2021 @04:09AM (#26099652)
> Yet the same be benefits of explicit None checks can be attained by writing "== None"

If you are going to do that's you should probably do a backwards comparison (`None==x`), otherwise you are calling x.__eq__(None), which probably won't be surprising in result if you have constrained things with sane typing, but still could be more expensive than `x is None`.

`x is None` reads a lot better though.

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