python - 请求/aiohttp : closing response objects

Question

我对在 requests 和 aiohttp 中都需要 .close() 响应对象感到有点困惑。 (请注意，这是一个独立于 session.close() 的实例方法——我说的是响应对象本身。)

• Response(requests)或ClientResponse(aiohttp)是否需要显式调用.close ()?
• 如果不是，将响应本身用作上下文管理器的目的是什么？ (与下面的 session.request('GET', 'https://www.pastebin.com') 异步。)如果它如下所示隐式关闭，为什么要为此定义两个 dunder 方法？

一些简单的测试(下面)似乎暗示响应在 session 上下文管理器内部定义时会自动关闭。(它本身调用 self.close() 在 __exit__ 或 __aexit__ 中。但这是 Session 的关闭，而不是 Response 对象。)

示例 - 请求

>>> import requests
>>> 
>>> with requests.Session() as s:
...     resp = s.request('GET', 'https://www.pastebin.com')
...     resp.raise_for_status()
...     print(resp.raw.closed)  # `raw` is urllib3.response.HTTPResponse object
...     print(resp.raw._pool)
...     print(resp.raw._connection)
...     c = resp.text
... 
True
HTTPSConnectionPool(host='pastebin.com', port=443)
None
>>>
>>> while 1:
...     print(resp.raw.closed)
...     print(resp.raw._pool)
...     print(resp.raw._connection)
...     break
... 
True
HTTPSConnectionPool(host='pastebin.com', port=443)
None

示例 - aiohttp

>>> import asyncio
>>> import aiohttp
>>>
>>> async def get():
...     async with aiohttp.ClientSession() as s:
...         # The response is already closed after this `with` block.
...         # Why would it need to be used as a context manager?
...         resp = await s.request('GET', 'https://www.pastebin.com')
...         print(resp._closed)
...         print(resp._connection)
...         print(resp._released)
...         c = await resp.text()
...     print()
...     print(resp._closed)
...     print(resp._connection)
...     print(resp._released)
...     return c
... 
>>> c = asyncio.run(get())  # Python 3.7 +
False
Connection<ConnectionKey(host='pastebin.com', port=443, is_ssl=True, ssl=None, proxy=None, proxy_auth=None, proxy_headers_hash=None)>
False

True
None
False

---

这是 requests.models.Response 的源代码。 “通常不需要明确调用”是什么意思？有哪些异常(exception)情况？

def close(self):
    """Releases the connection back to the pool. Once this method has been
    called the underlying ``raw`` object must not be accessed again.
    *Note: Should not normally need to be called explicitly.*
    """
    if not self._content_consumed:
        self.raw.close()

    release_conn = getattr(self.raw, 'release_conn', None)
    if release_conn is not None:
        release_conn()

Answer 1

请求:您无需显式调用close()。请求完成后会自动关闭，因为它基于urlopen(这就是为什么resp.raw.closed为True)，这是我观看session.py后的简化代码和适配器.py:

from urllib3 import PoolManager
import time
manager = PoolManager(10)
conn = manager.connection_from_host('host1.example.com')
conn2 = manager.connection_from_host('host2.example.com')
res = conn.urlopen(url="http://host1.example.com/",method="get")
print(len(manager.pools))
manager.clear()
print(len(manager.pools))
print(res.closed)

#2
#0
#True

那么 __exit__ 做了什么？它用于清除 PoolManager(self.poolmanager=PoolManager(...)) 和 proxy。

# session.py
def __exit__(self, *args): #line 423
    self.close()
def close(self): #line 733
    for v in self.adapters.values():
        v.close()

# adapters.py
# v.close()
def close(self): #line 307
        self.poolmanager.clear()
        for proxy in self.proxy_manager.values():
            proxy.clear()

所以什么时候应该使用 close() ，正如注释中所说的将连接释放回池，因为DEFAULT_POOLSIZE = 10(http/https 是独立的)。这意味着如果你想在一个 session 中访问超过 10 个网站，你可以选择关闭一些你不需要的网站，否则当你有一个 session 时，管理器将关闭从第一个到最新的连接。但实际上你不需要关心这个，你可以指定池大小并且不会浪费太多时间来重建连接

aiohttp aiohttp.ClientSession() 对所有请求使用一个 TCPConnector。当它触发 __aexit__ 时，self._connector 将被关闭。

编辑:s.request() 建立了来自主机的连接，但没有得到响应。 await resp.text()只有得到响应后才能执行，如果不执行此步骤(等待响应)，则无响应退出。

if connector is None: #line 132
    connector = TCPConnector(loop=loop)
...
self._connector = connector #line 151
# connection timeout
try:
    with CeilTimeout(real_timeout.connect,loop=self._loop):
    assert self._connector is not None
    conn = await self._connector.connect(
        req,
        traces=traces,
        timeout=real_timeout
        )
...
async def close(self) -> None:
        if not self.closed:
            if self._connector is not None and self._connector_owner:
                self._connector.close()
            self._connector = None
...
async def __aexit__(self,
                       ...) -> None:
        await self.close()

这是显示我所说内容的代码

import asyncio
import aiohttp
import time

async def get():
    async with aiohttp.ClientSession() as s:
        # The response is already closed after this `with` block.
        # Why would it need to be used as a context manager?
        resp = await s.request('GET', 'https://www.stackoverflow.com')
        resp2 = await s.request('GET', 'https://www.github.com')
        print("resp:",resp._closed)
        print("resp:",resp._connection)
        print("resp2:",resp2._closed)
        print("resp2:",resp2._connection)
        s.close()
        print(s.closed)
        c = await resp.text()
        d = await resp2.text()

    print()
    print(s._connector)
    print("resp:",resp._closed)
    print("resp:",resp._connection)
    print("resp2:",resp2._closed)
    print("resp2:",resp2._connection)

loop = asyncio.get_event_loop()
loop.run_until_complete(get())  # Python 3.5 +

#dead loop