python - 如何测试 python 类型协议(protocol)是另一个协议(protocol)的子类？

Question

该问题的明显解决方案是使用 issubclass，但这会引发 TypeError(使用 Python 3.6.7)，例如

>>> from typing_extensions import Protocol
>>> class ProtoSubclass(Protocol):
...     pass
... 
>>> issubclass(ProtoSubclass, Protocol)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/opt/conda/envs/airflow/lib/python3.6/site-packages/typing_extensions.py", line 1265, in __subclasscheck__
    raise TypeError("Instance and class checks can only be used with"
TypeError: Instance and class checks can only be used with @runtime protocols
>>> from typing_extensions import runtime
>>> @runtime
... class ProtoSubclass(Protocol):
...     pass
... 
>>> issubclass(ProtoSubclass, Protocol)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/opt/conda/envs/airflow/lib/python3.6/site-packages/typing_extensions.py", line 1265, in __subclasscheck__
    raise TypeError("Instance and class checks can only be used with"
TypeError: Instance and class checks can only be used with @runtime protocols

Answer 1

所选答案虽然没有错误，但并没有反射(reflect)提供结构子类型的Protocol的实际使用。 Python 3 始终可以使用名义子类型。

from typing import Protocol, runtime_checkable

@runtime_checkable
class Closable(Protocol):
    def close(self):
        ...

class AnyClass:
    def close(self):
        ...

issubclass(AnyClass, Closable)
#> True

此外，仅在基类中需要 runtime_checkable，即使正在检查的类是 Protocol 子类。

class ExtendedProtocol(Closable, Protocol):
    ...

class AnotherProtocol(Protocol):
    def close(self):
        ...

class NotAProtocol(Closable):
    # just inherits the protocol's default implementation
    ...

issubclass(ExtendedProtocol, Closable)
#> True
issubclass(AnotherProtocol, Closable)
#> True
issubclass(NotAProtocol, Closable)
#> True