backports_abc.py 文件源码

def mk_awaitable():
    from abc import abstractmethod, ABCMeta

    @abstractmethod
    def __await__(self):
        yield

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

    # calling metaclass directly as syntax differs in Py2/Py3
    Awaitable = ABCMeta('Awaitable', (), {
        '__slots__': (),
        '__await__': __await__,
        '__subclasshook__': __subclasshook__,
    })

    return Awaitable