在 Python 中使用嵌套类进行异步设计模式

Question

我在个人项目中遇到问题。 我开发了一个类来封装一个使用aiohttp的 Http 客户端，因此它使用异步代码。

我有几个类（与不同的 REST 服务相关）通过组合使用此客户端。 在服务类的每个方法中，我都调用了 http 客户端。 Http 客户端的代码如下所示（我已经简化了示例）：

class HttpClientSession:
    """
    This class is used to interfacing Http server.
    """

    def __init__(
        self,
        http_url: str,
        auth: Optional[BasicAuth] = None,
    ):
        """
        Constructs the Http client.

        :param http_url: URL to connect to Http server.
        :param auth: Authentication to connect to server.
        :raises Exception: If URL is empty.
        """
        logger.debug("Create Http client")

        if not http_url:
            raise Exception("Http URL is invalid")
        self._url: str = http_url

        #: Server authentication
        self._auth: Optional[BasicAuth] = auth

        #: HTTP session
        self._session: Optional[ClientSession] = None

        logger.debug("Http client created")

    async def __aenter__(self):
        """
        Create Http session to send requests.
        """
        self._session = ClientSession(
            auth=self._auth,
            raise_for_status=True,
            connector=TCPConnector(limit=50),
        )
        return self

    async def __aexit__(self, *err):
        """
        Close Http session.
        """
        await self._session.close()
        self._session = None

    async def get(self, suffix_url: str, headers: dict, query: Any = None):
        """
        Send a GET request.

        :param suffix_url: Last part of the URL contains the request.
        :param headers: Header for the request.
        :param query: Query of the request.
        :return: Response.
        """
        async with self._session.get(
            url=self._url + suffix_url,
            headers=headers,
            params=query,
        ) as response:
            return await response.json()

class HttpClient:
    """
    This class is used to interfacing Http server.
    """

    def __init__(
        self,
        http_url: str,
        auth: Optional[BasicAuth] = None,
    ):
        """
        Constructs the Http client.

        :param http_url: URL to connect to Http server.
        :param auth: Authentication to connect to server.
        :raises Exception: If URL is empty.
        """
        logger.debug("Create Http client")

        #: HTTP session
        self._session: HttpClientSession = HttpClientSession(http_url, auth)

        logger.debug("Http client created")

    async def get(self, suffix_url: str, headers: dict, query: Any = None):
        """
        Send a GET request.

        :param suffix_url: Last part of the URL contains the request.
        :param headers: Header for the request.
        :param query: Query of the request.
        :return: Response.
        """
        async with self._session as session:
            return await session.get(suffix_url,headers, query)

为了提高效率，我希望能够重用 Http Session 这就是为什么我创建了一个会话类，它允许我使用调用者使用异步语法，但如果不需要，调用者可以直接调用HttpClient创建专用会话的方法。

所以这很方便，因为我可以写：

http_client = HttpClient(...)
http_client.get(...)

要么

http_client = HttpClient(...)
async with http_client as http_session:
    http_session.get(...)
    http_session.get(...)

它工作得很好，但现在我的问题是我想为服务类的用户做同样的事情，以便也能够重用会话或不重用会话。 我有点卡住了，但我的目的是也有这个语法：

client = ServiceClient(...)
client.do_something(...)  # do_something will call http_client.get(...)

要么

client = ServiceClient(...)
async with client as session:
    session.do_something(...) # do_something will call http_session.get(...)
    session.do_something_else(...)  # do_something_else will reuse http_session

但我不想每次都这样做：

client = ServiceClient(...)
async with client as session:
    session.do_something(...) # session is not reuse so I don't want boilerplate of async with

我试图定义__aenter__方法，但我还没有找到避免代码重复的优雅方法。

你有什么想法吗？

我试图在服务类中添加HttpClient和HttpClientSession类中使用的相同模式，但没有成功让ServiceClient调用HttpClient和ServiceClientSession调用HttpClientSession 。

事实上，我什至不确定这样做是否是更好的模式。

Answer 1

我找到了一种解决方案。

对于HttpClient ，我重构以删除HttpClientSession类并管理可选会话：

class HttpClient:
    """
    This class is used to interfacing Http server.
    """

    def __init__(
        self,
        http_url: str,
        auth: Optional[BasicAuth] = None,
    ):
        """
        Constructs the Http client.

        :param http_url: URL to connect to Http server.
        :param auth: Authentication to connect to server.
        :raises Exception: If URL is empty.
        """
        logger.debug("Create Http client")

        if not http_url:
            raise Exception("Http URL is invalid")
        self._url: str = http_url

        #: Server authentication
        self._auth: Optional[BasicAuth] = auth

        #: HTTP session
        self._session: Optional[ClientSession] = None

        logger.debug("Http client created")

    async def __aenter__(self):
        """
        Create Http session to send requests.
        """
        self._session = ClientSession(
            auth=self._auth,
            raise_for_status=True,
            connector=TCPConnector(limit=50),
        )
        return self

    async def __aexit__(self, *err):
        """
        Close Http session.
        """
        await self._session.close()
        self._session = None

    async def get(self, suffix_url: str, headers: dict, query: Any = None):
        """
        Send a GET request.

        :param suffix_url: Last part of the URL contains the request.
        :param headers: Header for the request.
        :param query: Query of the request.
        :return: Response.
        """
        if self._session:
            async with self._session.get(
                    url=self._url + suffix_url,
                    headers=headers,
                    params=query,
            ) as response:
                return await response.json()
        else:
            async with ClientSession(
                auth=self._auth,
                raise_for_status=True,
                connector=TCPConnector(limit=50),
            ) as session:
                async with session.get(
                    url=self._url + suffix_url,
                    headers=headers,
                    params=query,
                ) as response:
                    return await response.json()

在服务类中，我还定义了支持异步语法的方法：

    async def __aenter__(self):
        """
        Create session to send requests.
        """
        await self._http_client.__aenter__()
        return self

    async def __aexit__(self, *err):
        """
        Close session.
        """
        await self._http_client.__aexit__(*err)

所以它有效，但我不知道是否有更好的方法，因为我不喜欢 if-else 语句。