如果value1==value2在python中不是None，compare如何工作？

Question

我发现了

a == b is not None

比较a == b，如果为真，则执行b is not None。你知道吗

(a == b) is not None  

以及

a == (b is not None)

我在哪里可以找到更多关于这种行为的信息？ 它非常简单，但我希望True is not None被执行

Answer 1

语言参考6.10. Comparisons中记录了这一点：

Unlike C, all comparison operations in Python have the same priority, which is lower than that of any arithmetic, shifting or bitwise operation. Also unlike C, expressions like a < b < c have the interpretation that is conventional in mathematics:

comparison    ::=  or_expr (comp_operator or_expr)*
comp_operator ::=  "<" | ">" | "==" | ">=" | "<=" | "!="
                   | "is" ["not"] | ["not"] "in"

Comparisons yield boolean values: True or False.

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).

==和is not都是比较运算符，因此它们是如上所述的链。你知道吗