我想创建一个使用aiohttp进行API调用的调度程序类。我尝试过这个:
I would like to create a scheduler class that uses aiohttp to make API calls. I tried this:
import asyncio import aiohttp class MySession: def __init__(self): self.session = None async def __aenter__(self): async with aiohttp.ClientSession() as session: self.session = session return self async def __aexit__(self, exc_type, exc_val, exc_tb): if self.session: await self.session.close() async def method1(): async with MySession() as s: async with s.session.get("www.google") as resp: if resp.status == 200: print("successful call!") loop = asyncio.get_event_loop() loop.run_until_complete(method1()) loop.close()但这只会导致错误: RuntimeError:会话已关闭。 __ aenter __ 函数的第二种方法:
but this just results in an error: RuntimeError: Session is closed. A second approach for the __aenter__ function:
async def __aenter__(self): self.session = aiohttp.ClientSession() return self效果很好。这是一个好结构吗?它不遵循有关如何使用aiohttp的示例。还想知道为什么第一种方法不起作用?
works well. Is this a good construct? It doesn't adhere to examples of how to use aiohttp. Also wondering why the first approach isn't working?
推荐答案您不能在中使用在函数内并让上下文管理器保持打开状态,否。当您使用 return 退出<$时,带有aiohttp.ClientSession()作为会话的退出: c $ c> __ aenter __ 协程!
You can't use with inside a function and have the context manager remain open, no. The with with aiohttp.ClientSession() as session: block exits as soon as you use return to exit the __aenter__ coroutine!
在特定情况下,输入 aiohttp.ClientSession()上下文管理器除了返回自我 。因此,对于那个类型,只需创建实例并将其存储在 self.session 中,然后等待 self.session。 close()在这里就足够了,是的。
For the specific case, entering a aiohttp.ClientSession() context manager does nothing but return self. So for that type, just creating the instance and storing it in self.session, and awaiting on self.session.close() suffices here, yes.
嵌套异步上下文管理器的 general 模式将等待嵌套异步上下文管理器的 __ aenter __ 和 __ aexit __ 方法来自您自己的此类方法(并且可能会传递异常信息) :
The general pattern for a nested asynchronous context manager is to await the __aenter__ and __aexit__ methods of a nested async context manager from your own such methods (and perhaps pass along the exception information):
class MySession: def __init__(self): self.session = None async def __aenter__(self): self.session = aiohttp.ClientSession() await self.session.__aenter__() return self async def __aexit__(self, exc_type, exc_val, exc_tb): if self.session: return await self.session.__aexit__(exc_type, exc_val, exc_tb)从技术上讲,您首先应该确保 __ aexit __ 属性,然后进入嵌套上下文管理器:
Technically speaking, you should first assure that there is an actual __aexit__ attribute before entering a nested context manager:
class MySession: def __init__(self): self.session = None self._session_aexit = None async def __aenter__(self): self.session = aiohttp.ClientSession() self._session_aexit = type(self.session).__aexit__ await self.session.__aenter__() return self async def __aexit__(self, exc_type, exc_val, exc_tb): if self.session: return await self._session_aexit.__aexit__( self.session, exc_type, exc_val, exc_tb)请参见 。异步Context-managers-and-async-with rel = noreferrer>添加了该概念的官方PEP 。
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