4 ms·

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, pref

• shoo 6y ago
  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.
  • pansa2 6y ago
    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
    • eirki 6y ago
      It is also marginally faster, I think.
      • dagw 6y ago
        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
  • dragonwriter 6y ago
    > 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.
• deleted 6y ago
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