我正在尝试使用asyncio和aiohttp加速对Web服务的多个get请求。
为此，我使用函数内的psycopg2模块.fetchmany（）从Postgresql数据库中获取我的数据，并构造了100条记录的字典，作为字典URL列表发送到名为batch（）的异步函数。逐批处理。
batch（）函数面临的问题是，尽管脚本继续执行并且不会失败，但是某些请求正在记录以下消息，但是我无法捕获并记录此异常以供以后重新处理。
Task exception was never retrieved
future: <Task finished coro=<batch.<locals>.fetch() done, defined at C:/PythonProjects/bindings/batch_fetch.py:34> exception=ClientOSError(10054, 'An existing connection was forcibly closed by the remote host', None, 10054, None)>
Traceback (most recent call last):
File "C:/PythonProjects/bindings/batch_fetch.py", line 36, in fetch
async with session.get(url) as resp:
File "C:\Miniconda3\lib\site-packages\aiohttp\client.py", line 1005, in __aenter__
self._resp = await self._coro
File "C:\Miniconda3\lib\site-packages\aiohttp\client.py", line 497, in _request
await resp.start(conn)
File "C:\Miniconda3\lib\site-packages\aiohttp\client_reqrep.py", line 844, in start
message, payload = await self._protocol.read() # type: ignore # noqa
File "C:\Miniconda3\lib\site-packages\aiohttp\streams.py", line 588, in read
await self._waiter
aiohttp.client_exceptions.ClientOSError: [WinError 10054] An existing connection was forcibly closed by the remote host
Task exception was never retrieved
future: <Task finished coro=<batch.<locals>.fetch() done, defined at C:/PythonProjects/bindings/batch_fetch.py:34> exception=ClientConnectorError(10060, "Connect call failed ('xx.xxx.xx.xxx', 80)")>
Traceback (most recent call last):
File "C:\Miniconda3\lib\site-packages\aiohttp\connector.py", line 924, in _wrap_create_connection
await self._loop.create_connection(*args, **kwargs))
File "C:\Miniconda3\lib\asyncio\base_events.py", line 778, in create_connection
raise exceptions[0]
File "C:\Miniconda3\lib\asyncio\base_events.py", line 765, in create_connection
yield from self.sock_connect(sock, address)
File "C:\Miniconda3\lib\asyncio\selector_events.py", line 450, in sock_connect
return (yield from fut)
File "C:\Miniconda3\lib\asyncio\selector_events.py", line 480, in _sock_connect_cb
raise OSError(err, 'Connect call failed %s' % (address,))
TimeoutError: [Errno 10060] Connect call failed ('xx.xxx.xx.xxx', 80)
The above exception was the direct cause of the following exception:
Traceback (most recent call last):
File "C:/PythonProjects/bindings/batch_fetch.py", line 36, in fetch
async with session.get(url) as resp:
File "C:\Miniconda3\lib\site-packages\aiohttp\client.py", line 1005, in __aenter__
self._resp = await self._coro
File "C:\Miniconda3\lib\site-packages\aiohttp\client.py", line 476, in _request
timeout=real_timeout
File "C:\Miniconda3\lib\site-packages\aiohttp\connector.py", line 522, in connect
proto = await self._create_connection(req, traces, timeout)
File "C:\Miniconda3\lib\site-packages\aiohttp\connector.py", line 854, in _create_connection
req, traces, timeout)
File "C:\Miniconda3\lib\site-packages\aiohttp\connector.py", line 992, in _create_direct_connection
raise last_exc
File "C:\Miniconda3\lib\site-packages\aiohttp\connector.py", line 974, in _create_direct_connection
req=req, client_error=client_error)
File "C:\Miniconda3\lib\site-packages\aiohttp\connector.py", line 931, in _wrap_create_connection
raise client_error(req.connection_key, exc) from exc
aiohttp.client_exceptions.ClientConnectorError: Cannot connect to host cms-uat.cme.in.here.com:80 ssl:None [Connect call failed ('xx.xxx.xx.xxx', 80)]
正如我可以从我的代码中描绘的那样，我刚刚进入异步世界，因此，针对这种情况的完整代码方法的所有建议都非常欢迎。
谢谢
下面的完整代码。
import psycopg2.extras
import asyncio
import json
from aiohttp import ClientSession
from aiohttp import TCPConnector
base_url = 'http://url-example/{}'
def query_db():
urls = []
# connection to postgres table , fetch data.
conn = psycopg2.connect("dbname='pac' user='user' host='db'")
cursor = conn.cursor('psycopg2 request', cursor_factory=psycopg2.extras.NamedTupleCursor)
sql = "select gid, paid from table"
cursor.execute(sql)
while True:
rec = cursor.fetchmany(100)
for item in rec:
record = {"gid": item.gid, "url": base_url.format(item.paid)}
urls.append(record.get('url'))
if not rec:
break
# send batch for async batch request
batch(urls)
# empty list of urls for new async batch request
urls = []
def batch(urls):
async def fetch(url):
async with ClientSession() as session:
async with session.get(url) as resp:
if resp.status == 200:
response = await resp.json()
# parse the url to fetch the point address id.
paid = str(resp.request_info.url).split('/')[4].split('?')[0]
# build the dictionary with pa id and full response.
resp_dict = {'paid': paid, 'response': response}
with open('sucessful.json', 'a') as json_file:
json.dump(resp_dict, json_file)
json_file.write("\n")
elif resp.status is None:
print(resp.status)
elif resp.status != 200:
print(resp.status)
response = await resp.json()
# parse the url to fetch the paid.
paid = str(resp.request_info.url).split('/')[4].split('?')[0]
# build the dictionary with paid and full response.
resp_dict = {'paid': paid, 'response': response}
with open('failed.json', 'a') as json_file:
json.dump(resp_dict, json_file)
json_file.write("\n")
loop = asyncio.get_event_loop()
tasks = []
for url in urls:
task = asyncio.ensure_future(fetch(url))
tasks.append(task)
try:
loop.run_until_complete(asyncio.wait(tasks))
except Exception:
print("exception consumed")
if __name__ == "__main__":
query_db()
答案 0 :(得分：1)
从未检索到任务异常
创建某些任务时，您会看到此警告，该任务以异常结束，但是您从未明确检索（等待）其结果。这是与doc section相关的。
我敢打赌，你的问题是线路
loop.run_until_complete(asyncio.wait(tasks))
asyncio.wait() by default仅在所有tasks完成后等待。它不能区分正常完成的任务还是异常完成的任务，它只是阻塞直到一切完成为止。在这种情况下，从完成的任务中检索异常是您的工作，而下一部分将无济于事，因为asyncio.wait()永远不会引发错误：
try:
loop.run_until_complete(asyncio.wait(tasks))
except Exception:
print('...') # You will probably NEVER see this message
如果您想在一项任务中立即发现错误，我建议您使用asyncio.gather()。 By default将引发第一次发生的异常。但是请注意，如果要正常关闭cancel个待处理的任务，这是您的工作。