如何参数化 Python 中的 mixin 类？

Question

我正在开发一个BaseServer摘要 class：

class BaseServer(abc.ABC):

    @abc.abstractmethod
    def serve(self):
        raise NotImplementedError

    @abc.abstractmethod
    def shutdown(self):
        raise NotImplementedError

    @abc.abstractmethod
    def send(self, *args, **kwargs):
        raise NotImplementedError

    @abc.abstractmethod
    def finalise(self, *args, **kwargs):
        raise NotImplementedError

    @abc.abstractmethod
    def is_serving(self):
        raise NotImplementedError

    def set_handler(self, handler):
        self.__handler = handler

    def _handle(self, *args, **kwargs):
        try:
            self.__handler.handle(self, *args, **kwargs)
        except AttributeError:
            pass

    def _cleanup(self):
        pass

以及ThreadPoolMixin和ProcessPoolMixin混合类（灵感来自 Python 的socketserver模块）：

class ThreadPoolMixin:

    def _handle(self, *args, **kwargs):
        try:
            future = self.__pool.submit(super()._handle, *args, **kwargs)
            self.__futures.append(future)
        except AttributeError:
            self.__pool = concurrent.futures.ThreadPoolExecutor(1)
            self.__futures = []
            future = self.__pool.submit(super()._handle, *args, **kwargs)
            self.__futures.append(future)

    def _cleanup(self):
        try:
            for future in self.__futures:
                future.cancel()

            self.__pool.shutdown()
        except AttributeError:
            pass


class ProcessPoolMixin:

    def _handle(self, *args, **kwargs):
        try:
            future = self.__pool.submit(super()._handle, *args, **kwargs)
            self.__futures.append(future)
        except AttributeError:
            self.__pool = concurrent.futures.ProcessPoolExecutor(1)
            self.__futures = []
            future = self.__pool.submit(super()._handle, *args, **kwargs)
            self.__futures.append(future)

    def _cleanup(self):
        try:
            for future in self.__futures:
                future.cancel()

            self.__pool.shutdown()
        except AttributeError:
            pass

    def __getstate__(self):
        class Temp:
            pass

        state = self.__dict__.copy()
        temp = Temp()
        temp.__dict__ = state

        try:
            del temp.__pool
            del temp.__futures
        except AttributeError:
            pass

        return temp.__dict__

这些类允许我根据需要创建具体的子类：

class HTTPServer(BaseServer):
    pass


class AMQPServer(BaseServer):
    pass


class ThreadingHTTPServer(ThreadPoolMixin, BaseServer):
    pass


class ThreadingAMQPServer(ThreadPoolMixin, BaseServer):
    pass


class ProcessingHTTPServer(ProcessPoolMixin, BaseServer):
    pass


class ProcessingAMQPServer(ProcessPoolMixin, BaseServer):
    pass

如何从这些子类自定义线程池大小和进程池大小？

Answer 1

我想出了一个解决方案：使用公共类属性，就像在socketserver.ThreadingMixIn和socketserver.ForkingMixIn 。

class ThreadPoolMixin:
    pool_size = 1

    def _handle(self, *args, **kwargs):
        try:
            future = self.__pool.submit(super()._handle, *args, **kwargs)
            self.__futures.append(future)
        except AttributeError:
            self.__pool = concurrent.futures.ThreadPoolExecutor(
                self.pool_size)
            self.__futures = []
            future = self.__pool.submit(super()._handle, *args, **kwargs)
            self.__futures.append(future)

    def _cleanup(self):
        try:
            for future in self.__futures:
                future.cancel()

            self.__pool.shutdown()
        except AttributeError:
            pass


class ThreadingHTTPServer(ThreadPoolMixin, BaseServer):
    pool_size = 4


class ThreadingAMQPServer(ThreadPoolMixin, BaseServer):
    pool_size = 2

Answer 2

我正在试验的另一种方法是“mixin 工厂”，它根据需要创建新的 mixin 类：

def thread_pool_mixin(pool_size: int) -> Type:
    class ThreadPoolMixin:
        def _handle(self, *args, **kwargs):
            . . .
            # Use the closed-over "pool_size"
            self.__pool = concurrent.futures.ThreadPoolExecutor(pool_size)
            . . .
    return ThreadPoolMixin


class ThreadingHTTPServer(thread_pool_mixin(pool_size=4), BaseServer):
    pass

这似乎比混淆 class 属性更干净； 尽管这似乎是常见的方法。