集合操作：只适用于集合，但适用于 dict_keys？

Question

Note, the non-operator versions of union(), intersection(), difference(), symmetric_difference(), issubset(), and issuperset() methods will accept any iterable as an argument. In contrast, their operator based counterparts require their arguments to be sets. This precludes error-prone constructions like set('abc') & 'cbs' in favor of the more readable set('abc').intersection('cbs').

通过以下实验对此进行测试：

# Python 3.10.2 (main, Jan 15 2022, 19:56:27) [GCC 11.1.0] on linux

>>> set('ab') & set('ac')
{'a'}
# works, as expected

>>> set('ab') & 'ac'
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: unsupported operand type(s) for &: 'set' and 'str'
# doesn't work, as expected

>>> set('ab') & list('ac')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: unsupported operand type(s) for &: 'set' and 'list'
# doesn't work, as expected

>>> set('ab') & iter('ac')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: unsupported operand type(s) for &: 'set' and 'str_iterator'
# doesn't work, as expected

>>> set('ab') & dict(zip('ac', 'ac')).keys()
{'a'}
# works??

>>> type({}.keys())
<class 'dict_keys'>

>>> isinstance({}.keys(), (set, frozenset))
False

所以，这是悖论：

set 运算符 & 适用于 dict_keys 个对象；
文档说它应该只适用于集合；
dict_keys 对象不是集合。

为什么集合运算符 & 与 dict_keys 对象一起使用？它还有其他类型吗？我怎样才能找到这些类型的列表？

Answer 1

这不是一个完整的答案，但 dict_keys 是 collections.abc.Set 的实例：

from collections.abc import Set
k = dict(zip('ac', 'ac')).keys()
print(isinstance(k, Set))  # -> True

集合操作：只适用于集合，但适用于 dict_keys？

Set operations: should only work with sets, but works with dict_keys?

dictionary

set

python-3.x