WTF Python: Exploring and understanding Python through surprising snippets

Re:WTF Python: Exploring and understanding Python through su... by j0057 on Thursday February 11, 2021 @03:22AM (#26099426)

Python should just remove the `is` operator. If you really need to compare object identities, which is already a rare scenario to begin with, you can explicitly compare the object IDs. Checking if something is or is not True/False/None can just be treating the thing as True-ish or False-ish. Making the language bigger is not nearly as impressive as making it smaller!

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Re:WTF Python: Exploring and understanding Python through su... by dagw on Thursday February 11, 2021 @03:33AM (#26099474)

I find checking for "is None" very useful, but that is also the only time I use 'is'. I try to avoid checking for True-ish and False-ish whenever possible, preferring to be more explicit.

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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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Re:WTF Python: Exploring and understanding Python through su... by pansa2 on Thursday February 11, 2021 @03:49AM (#26099555)

Yeah, IME `is None` is by far the most common use of `is`. I don’t think many people would miss `is` if it were removed and an `is_none` function introduced.

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Re:WTF Python: Exploring and understanding Python through su... by dragonwriter on Thursday February 11, 2021 @03:59AM (#26099603)

> Checking if something is or is not True/False/None can just be treating the thing as True-ish or False-ish.

No, it can't. Especially obviously not something whose type is Optional[bool]. Or, more subtly, Optional[Number] or Optional[Sequence[T]].

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