python 运算符优先级如何与双重比较一起使用？

Question

-3<-2<-1 returns True.

但是我希望它被解释为

(-3<-2)<-1
True<-1
1<-1
False

这怎么可能？

Answer 1

From the docs:

Unlike C, expressions like a < b < c have the interpretation that is conventional in mathematics

Comparisons can be chained arbitrarily, e.g., x < y <= z is equivalent to x < y and y <= z, except that y is evaluated only once (but in both cases z is not evaluated at all when x < y is found to be false).

因此

-3 < -2 < -1  

等同于

-3 < -2 and -2 < -1  # where -2 is evaluated only once

Answer 2

在documentation中声明它是语言的一部分

Answer 3

这是一个chained comparison。它不是像 (-3 < -2) < -1 这样的左结合或像 -3 < (-2 < -1) 这样的右结合，而是实际上被视为

(-3 < -2) and (-2 < -1)

除了 -2 最多计算一次。