7 ms·

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

by j0057 6y ago

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!

dagw 6y ago
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.
- 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
  [deleted]
pansa2 6y ago
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.
dragonwriter 6y ago
> 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]].

by j0057 6y ago

dagw 6y ago

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.

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
[deleted]

pansa2 6y ago

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.

dragonwriter 6y ago

> 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]].