如果 value1 == value2 不是 python 中的 None，比较如何工作？

Question

我发现

a == b is not None

比较a == b，如果为真则执行b is not None。

(a == b) is not None

和

a == (b is not None)

在哪里可以找到有关此类行为的更多信息？这很简单，但我希望 True is not None 被执行

Answer 1

这在语言参考中有记载，6.10. Comparisons:

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，因此它们按上述方式链接。

如果 value1 == value2 不是 python 中的 None，比较如何工作？

How does compare work if value1 == value2 is not None in python?

python

logical-operators