围绕嵌套函数定义上下文管理器是否安全？

发布于 2025-01-10 05:49:38 字数 523 浏览 3 评论 0原文

对于第三方库*，我必须提供一个消耗一些数据的函数。我的消费实现需要将数据发布到 API。所以我想出了下面的结构：

def consumer_provider():

    with HttpClient() as http_client:
        
        def consumer(data):
            http_client.post(data)

        return consumer

所以我可以像这样向第三方库展示该函数：

third_party_lib.add(consumer=consumer_provider())

在我的测试中它工作得很好，但是这是合法的吗？我什么时候必须期望上下文管理器释放资源（在本例中为连接池）？

* 在这种情况下是 loguru，但这对于问题来说并不重要

原文

For a third party library* I have to provide a function which consumes some data. My implementation of the consumption requires the data to be posted to an API. So I came up with this structure below:

def consumer_provider():

    with HttpClient() as http_client:
        
        def consumer(data):
            http_client.post(data)

        return consumer

So I can present the function to the third party lib like so:

third_party_lib.add(consumer=consumer_provider())

In my tests it works quite well, but is this legit? When do I have to expect that the context manager releases the resource (in this case the connection pool)?

* loguru in this case, but it should not really matter for the question

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提笔落墨 2025-01-17 05:49:38

这取决于上下文管理器。在您编写的代码中，您创建的 HTTPClient 保持活动状态，因为它返回的函数保留对它的引用，即使 consumer_provider 中定义的变量 http_client 也是如此。 code> 超出范围。

但是，在 consumer_provider 返回之前仍会调用 HTTPClient.__exit__，因此消费者函数可能无法按预期工作。

您可能想要执行类似的操作

def consumer_provider():
    http_client = HttpClient()
    def consumer(data):
        with http_client:
            http_client.post(data)
    return consumer

，以确保 HttpClient 对象在闭包内保持“隐藏”状态，但其 __enter__ 和 __exit__ 方法不是' t 被调用直到函数被调用。（客户端是否可以被多个函数调用使用还取决于HttpClient的定义。）

It depends on the context manager. In the code you wrote, the HTTPClient you created stays alive because the function it returns maintains a reference to it, even though the variable http_client defined in consumer_provider goes out of scope.

However, HTTPClient.__exit__ is still called before consumer_provider returns, so the consumer function may not work as intended.

You may want to do something like

def consumer_provider():
    http_client = HttpClient()
    def consumer(data):
        with http_client:
            http_client.post(data)
    return consumer

which ensures that the HttpClient object stays "hidden" inside the closure, but its __enter__ and __exit__ methods aren't called until the function gets called. (Whether the client can be used by multiple function calls also depends on the definition of HttpClient.)

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