Usefulness of the "not in" operator
mail.python.org
mail.python.org
They use a veiled slippery slope argument; 'if we did that, we might as well use not and >='. Well no, when you say something is less you don't say "not greater than or equal", in English those two sentences sound different even if their net meaning is the same. With != vs not ==, that would be awful not because not == is inherently bad looking, but because precedence levels would force you to use parenthesis every single time; in doesn't suffer from this problem since it is higher precedence than not. With !=, you avoid 5 or 7 tangled characters with 2 simple characters. With "not in" you are adding something to the language so you can type 5 simple characters instead of the same 5 simple characters in a slightly different order.
You could just as easily go the opposite direction and say 'if we are going to have a 'not in' operator, why not have "unless" that is the equivalent to "if not", why not have an "until" keyword that is the same as "while not"?
Is there any legitimate claim to be made about how "until" in VB is widely accepted to be awful but "not in" in python is beautiful?
if not x in y:
...
if (not x) in y:
...
if not (x in y):
...
It's not identical. Their effects are identical --which is a different thing.
With turing completeness you could do with even less, but that's not the point.
The point is: "x not in y" is more natural -- and Python is praised for it's ability to read like natural language/pseudocode (which it doesn't always achieve, but this is one case that it does).
We say: "if my tie is not in the suitcase, do something".
We don't say: "if not is my tie in the suitecase, do something" (except Yoda).
You completely did not respond to what I wrote; I say "until and unless are just as much more natural compared to the way you currently implement them, as (x not in y) is compared (not x in y)" and you say "(x not in y) is natural!". That doesn't show my claim isn't true, to be an argument against my claim you have to also claim that people don't say "until you are done, do next thing". Or that people don't say "do the next thing until you are done", or "bake cookies until done"; python has no do-while construct much less do-until.
So again; why is that "not in" is sufficiently important to be a language feature but do-until is hideous and unnatural?
The NAND and NOR functions, independently, are the most well-known functionally complete sets -- that is, all Boolean logic can be derived from each of those single Boolean functions.
I like "not in" and use it lots but I wondered the same thing the first time I saw it.