如何在 Python 中键入一个类的对象也遵守协议？

Question

我有一组类，我们称它们为Foo 和Bar，它们都继承自在当前范围之外（不是我）定义的基类Father。我已经定义了一个协议类DummyProtocol，它有一个函数do_something。

class DummyProtocol(Protocol):
   def do_something(self):
      ...
   

class Foo(Father):
   def do_something(self):
      pass

class Bar(Father):
   def do_something(self):
      pass

我有一个函数create_instance。

def create_dummy_and_father_instance(cls, *args, **kwargs):
    return cls(*args, **kwargs)

我想以某种方式输入提示，即 cls 被输入提示以接受 Father 类型的类，该类也实现了 DummyProtocol。

所以我把函数改成这个，表示cls是继承自Father和DummyProtocol的类型

def create_dummy_and_father_instance(
    cls: Type[tuple[Father, DummyProtocol]], *args, **kwargs
):
    return cls(*args, **kwargs)

但我在mypy 中收到此错误：

Cannot instantiate type "Type[Tuple[Father, DummyProtocol]]"

Answer 1

您可以定义第二个继承自父亲和协议的父亲类（另请参阅mypy: how to verify a type has multiple super classes）：

class DummyProtocol(Protocol):

    def do_something(self):
        ...
    
class Father:
    pass
    
class Father2(Father, DummyProtocol):
    pass
    
class Foo(Father2):

    def do_something(self):
        pass
    
class Bar(Father2):

    def do_something(self):
        pass
    
class FooNot(Father):
    pass
    
def create_dummy_and_father_instance(
    cls: Type[Father2]
):
    return cls()
    
create_dummy_and_father_instance(Foo)
create_dummy_and_father_instance(Bar)
create_dummy_and_father_instance(FooNot)  # mypy error ok