奇数运算符优先级/关联行为 [英] Odd operator precedence/associativity behaviour

问题描述

在python 2.7中，以下内容如何

How is it that, in Python 2.7, the following

True == 'w' in 'what!?'

行为不同于两者

(True == 'w') in 'what!?'

和

True == ('w' in 'what!?')

?

>>> True == 'w' in 'what!?'
False

>>> (True == 'w') in 'what!?'
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'in <string>' requires string as left operand, not bool

>>> True == ('w' in 'what!?')
True

推荐答案

在Python中，比较可以为链接在一起:

In Python, comparisons can be chained together:

比较可以任意链接，例如x

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).

所以您的代码实际上等效于

So your code is actually equivalent to

>>> (True == 'w') and ('w' in 'what!?')
False

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