Python collections.abc的实现不一致

我正在努力理解源代码

让我们看一看Hashable类的实现：

@classmethod
def __subclasshook__(cls, C):
    if cls is Hashable:
        for B in C.__mro__:
            if "__hash__" in B.__dict__:
                if B.__dict__["__hash__"]:
                    return True
                break
    return NotImplemented

在这里，我们首先检查是否存在属性

哈希

，然后检查它是否具有非false值。此逻辑也在

等待

类中提供

和

AsyncIterable

class'

\uuu子类hook\uuuu

：

@classmethod
def __subclasshook__(cls, C):
    if cls is AsyncIterable:
        if any("__aiter__" in B.__dict__ for B in C.__mro__):
            return True
    return NotImplemented

在这里，我们只需检查是否存在

\uuuuu aiter\uuuuuu

属性，并且该逻辑在该包中的任何其他类中显示

这种逻辑差异有什么原因吗？

通过设置

\uuuuu hash\uuuu=None

，显式允许将类标记为不可损坏

如果类[…]希望取消哈希支持，则应在类定义中包含

\uuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuu=None

---

原因是

a==b

总是需要

hash（a）==hash（b）

。否则，

dict

、

set

和类似的数据结构将中断。如果子类显式地或以其他方式更改

\uuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuueq

，则此。因此，

\uuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuu。提到“可等待的”

并不总能正常工作，因此ABC可能无法最终确定。严格地说，没有任何东西禁止其他ABC以任何方式检查

Hashable

。