python - 二元运算符应用于逻辑时意味着什么？

Question

我的理解是 & 是按位与运算符。所以我希望它在应用于逻辑时没有任何意义。但是，我看到了:

>>> False & False
False
>>> False & True
False
>>> True & True
True

等等。其他按位运算符也是如此。

那么，为什么这些运算符甚至接受逻辑操作数呢？我在哪里可以找到解释这个的文档？我搜索了它，但找不到解释。

Answer 1

So, why do these operators even accept logical operands?

bool 子类 int，并覆盖 __and__() 等以返回 bool for bool 操作数。

有关详细信息，请参阅 PEP 285 .

具体来说:

      6) Should bool inherit from int?       => Yes       In an ideal world, bool might be better implemented as a       separate integer type that knows how to perform mixed-mode       arithmetic.  However, inheriting bool from int eases the       implementation enormously (in part since all C code that calls       PyInt_Check() will continue to work -- this returns true for       subclasses of int).  Also, I believe this is right in terms of       substitutability: code that requires an int can be fed a bool       and it will behave the same as 0 or 1.  Code that requires a       bool may not work when it is given an int; for example, 3 & 4       is 0, but both 3 and 4 are true when considered as truth       values.

and

    class bool(int):

        def __and__(self, other):
            if isinstance(other, bool):
                return bool(int(self) & int(other))
            else:
                return int.__and__(self, other)

        __rand__ = __and__

        def __or__(self, other):
            if isinstance(other, bool):
                return bool(int(self) | int(other))
            else:
                return int.__or__(self, other)

        __ror__ = __or__

        def __xor__(self, other):
            if isinstance(other, bool):
                return bool(int(self) ^ int(other))
            else:
                return int.__xor__(self, other)

        __rxor__ = __xor__

注意 bool & bool 如何返回 bool 而 bool & non-bool 继承 int 的行为(即返回一个 int)。

以下是展示这些属性的一些示例:

In [12]: isinstance(True, int)
Out[12]: True

In [13]: True & True
Out[13]: True

In [14]: True & 1
Out[14]: 1

上述行为不适用于算术运算符。那些只是使用 int 的行为:

In [15]: True + 0
Out[15]: 1

In [16]: True + False
Out[16]: 1