python - @abstractmethod 在不应该使用 metaclass=ABCMeta 的情况下也能正常工作

Question

考虑这段代码

from abc import ABCMeta, abstractmethod

class C():
    @abstractmethod
    def my_abstract_method(self):
        print('foo')

class D(C):
    pass

x = C()
y = D()

mypy 不允许 x 和 y 产生我 a

test.py:13: error: Cannot instantiate abstract class 'C' with abstract attribute 'my_abstract_method'
test.py:15: error: Cannot instantiate abstract class 'D' with abstract attribute 'my_abstract_method'

我正在使用 mypy 0.570 和 python 3.6.3 进行测试

但是，文档说我需要设置 metaclass=ABCMeta 才能正常工作。我错过了什么？

Answer 1

好吧，事实证明，没有 metaclass=ABCMeta 时，只有 mypy 会捕获错误，而使用 metaclass=ABCMeta 时，mypy 和 python 将捕获错误。

参见:

from abc import abstractmethod

class C():
    @abstractmethod
    def my_abstract_method(self):
        print('foo')

class D(C):
    pass

x = C()
y = D()

$ mypy test.py 
test.py:13: error: Cannot instantiate abstract class 'C' with abstract attribute 'my_abstract_method'
test.py:15: error: Cannot instantiate abstract class 'D' with abstract attribute 'my_abstract_method'

但是

$ python3 test.py
$

然而，python 也会捕获错误。

from abc import ABCMeta, abstractmethod

class C(metaclass=ABCMeta):
    @abstractmethod
    def my_abstract_method(self):
        print('foo')

class D(C):
    pass

x = C()

y = D()


$ python3 test.py 
Traceback (most recent call last):
  File "test.py", line 11, in <module>
    x = C()
TypeError: Can't instantiate abstract class C with abstract methods my_abstract_method