[已解决]关于一个表达式的运算过程

御笔剑客

3>2>2最后输出的结果是False，它的运算过程是怎么样的呢？

最佳答案

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Amazon

2017-11-3 13:17:03

3>2>2
等价于
3>2 and 2>2
等价于
(3>2) and (2>2)

这就是所谓的“链式比较”。

这里有介绍：
- https://docs.python.org/3.6/reference/expressions.html

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).

Formally, if a, b, c, …, y, z are expressions and op1, op2, …, opN are comparison operators, then a op1 b op2 c ... y opN z is equivalent to a op1 b and b op2 c and ... y opN z, except that each expression is evaluated at most once.

Note that a op1 b op2 c doesn’t imply any kind of comparison between a and c, so that, e.g., x < y > z is perfectly legal (though perhaps not pretty).

- https://stackoverflow.com/questions/101268/hidden-features-of-python
  - https://stackoverflow.com/questions/101268/hidden-features-of-python#101945

跳转到最佳答案楼层

BngThea

python支持连续比较
内部会自动转换

比如
3>2>2 等价于：
3 > 2 and 2 > 2
返回 False

3>2>1 等价于：
3>2 and 2>1
返回True

Amazon

3>2>2
等价于
3>2 and 2>2
等价于
(3>2) and (2>2)

这就是所谓的“链式比较”。

这里有介绍：
- https://docs.python.org/3.6/reference/expressions.html

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).

Formally, if a, b, c, …, y, z are expressions and op1, op2, …, opN are comparison operators, then a op1 b op2 c ... y opN z is equivalent to a op1 b and b op2 c and ... y opN z, except that each expression is evaluated at most once.

Note that a op1 b op2 c doesn’t imply any kind of comparison between a and c, so that, e.g., x < y > z is perfectly legal (though perhaps not pretty).

- https://stackoverflow.com/questions/101268/hidden-features-of-python
  - https://stackoverflow.com/questions/101268/hidden-features-of-python#101945