Python 3.6.2 console:
>>> 11 > 0 is True
False
but
>>> 0 is True
False
>>> 11 > False
True
So, why 11 > 0 is True is False?
Asked
Active
Viewed 653 times
3
Alex
- 189
- 1
- 9
-
it's `(11>0) and (0 is True)`, I remember there is a dupe somewhere – apple apple Apr 18 '18 at 07:35
-
This behaviour seems really odd. – Aaron Christiansen Apr 18 '18 at 07:37
-
@AaronChristiansen yeah, this one is surprising if you are unaware that chaining applies to all comparison operators, not just `<` and `>` (and their inclusive versions). – juanpa.arrivillaga Apr 18 '18 at 07:40
-
@juanpa.arrivillaga The fact that Python can handle expressions like `2 < x < 5` is fantastic, but it feels a bit counterintuitive for `is`. – Aaron Christiansen Apr 18 '18 at 07:42
-
@AaronChristiansen I agree. But `is` should certainly be considered a comparison operator, and I'm not sure how I feel about this behavior only applying to *certain* comparison operators. Certainly, reasonable people could disagree. By now I'm just used to it. – juanpa.arrivillaga Apr 18 '18 at 07:45
1 Answers
4
This is an example of comparison chaining since both > and is are comparison operators.
Comparisons can be chained arbitrarily, e.g.,
x < y <= zis equivalent tox < y and y <= z, except thatyis evaluated only once (but in both caseszis not evaluated at all whenx < yis found to be false).Formally, if
a, b, c, …, y, zare expressions andop1, op2, …, opNare comparison operators, thena op1 b op2 c ... y opN zis equivalent toa op1 b and b op2 c and ... y opN z, except that each expression is evaluated at most once.
Thus, it is equivalent to:
>>> (11 > 0) and (0 is True)
False
juanpa.arrivillaga
- 88,713
- 10
- 131
- 172
-
2this one never gets old :) it's a duplicate, but hey, not all cases & combinations of `is`, `=`, `<`, `>` isn't covered and OPs don't have a clue of this chaining pattern and fail to see it most of the time. Every one of us should have a duplicate answer of that (I have one :)) – Jean-François Fabre Apr 18 '18 at 07:49
-
This particular case may take the prize for most naturally confusing combination though. `11 > 0 is True` is a nice sentence. – miradulo Apr 18 '18 at 07:53