如何要求抽象方法是协程？

Question

我如何要求抽象基类将特定方法实现为协程。例如，考虑这个 ABC：

import abc

class Foo(abc.ABC):
    @abc.abstractmethod
    async def func():
        pass

现在，当我子类化并实例化它时：

class Bar(Foo):
    def func():
        pass

b = Bar()

这成功了，尽管func不是async，就像在 ABC 中一样。我该怎么做才能使这仅在func是时成功async？

Answer 1

您可以使用__new__并检查子类是否以及如何覆盖父类的 coros。

import asyncio
import abc
import inspect


class A:    

    def __new__(cls, *arg, **kwargs):
        # get all coros of A
        parent_coros = inspect.getmembers(A, predicate=inspect.iscoroutinefunction)

        # check if parent's coros are still coros in a child
        for coro in parent_coros:
            child_method = getattr(cls, coro[0])
            if not inspect.iscoroutinefunction(child_method):
                raise RuntimeError('The method %s must be a coroutine' % (child_method,))

        return super(A, cls).__new__(cls, *arg, **kwargs)

    @abc.abstractmethod
    async def my_func(self):
        pass


class B(A):

    async def my_func(self):
        await asyncio.sleep(1)
        print('bb')


class C(A):

    def my_func(self):
        print('cc')

async def main():
    b = B()
    await b.my_func()

    c = C()  # this will trigger the RuntimeError
    await c.my_func()


loop = asyncio.get_event_loop()
loop.run_until_complete(main())

注意事项

• 子类也可以覆盖__new__以抑制此约束

• 不仅async可以等待。例如

  async def _change_in_db(self, key, value):
      # some db logic
      pass
  
  def change(self, key, value):
      if self.is_validate(value):
          raise Exception('Value is not valid')
      return self._change_in_db(key, value)  
  

  可以change这样打电话

  await o.change(key, value)
  

  更不用说__await__在对象、其他原始期货、任务中......