我想我想通过制作一个简单的脚本来学习新的 python async wait 语法，更具体地说是 asyncio 模块，该脚本允许您一次下载多个资源。
但现在我被困住了。
在研究时，我发现了两种限制并发请求数量的选项：
- 将 aiohttp.TCPConnector （带有 limit 参数）传递给 aiohttp.ClientSession 或
- 使用 asyncio.Semaphore。
如果您只想限制并发连接数，是否有首选选项或者可以互换使用它们？
就性能而言（大致）相同吗？
而且两者似乎都有 100 个并发连接/操作的默认值。如果我仅使用限制为 500 的信号量，aiohttp 内部是否会隐式将我锁定为 100 个并发连接？
这对我来说都是非常新的和不清楚的。请随时指出我的任何误解或代码中的缺陷。
这是我当前包含两个选项的代码（我应该删除哪个？）：
奖金问题：
- 如何处理（最好重试 x 次）抛出错误的 coros？
- coro 完成后立即保存返回数据（通知我的 DataHandler）的最佳方法是什么？我不希望最后保存所有内容，因为我可以尽快开始处理结果。
s
import asyncio
from tqdm import tqdm
import uvloop as uvloop
from aiohttp import ClientSession, TCPConnector, BasicAuth
# You can ignore this class
class DummyDataHandler(DataHandler):
"""Takes data and stores it somewhere"""
def __init__(self, *args, **kwargs):
super().__init__(*args, **kwargs)
def take(self, origin_url, data):
return True
def done(self):
return None
class AsyncDownloader(object):
def __init__(self, concurrent_connections=100, silent=False, data_handler=None, loop_policy=None):
self.concurrent_connections = concurrent_connections
self.silent = silent
self.data_handler = data_handler or DummyDataHandler()
self.sending_bar = None
self.receiving_bar = None
asyncio.set_event_loop_policy(loop_policy or uvloop.EventLoopPolicy())
self.loop = asyncio.get_event_loop()
self.semaphore = asyncio.Semaphore(concurrent_connections)
async def fetch(self, session, url):
# This is option 1: The semaphore, limiting the number of concurrent coros,
# thereby limiting the number of concurrent requests.
with (await self.semaphore):
async with session.get(url) as response:
# Bonus Question 1: What is the best way to retry a request that failed?
resp_task = asyncio.ensure_future(response.read())
self.sending_bar.update(1)
resp = await resp_task
await response.release()
if not self.silent:
self.receiving_bar.update(1)
return resp
async def batch_download(self, urls, auth=None):
# This is option 2: Limiting the number of open connections directly via the TCPConnector
conn = TCPConnector(limit=self.concurrent_connections, keepalive_timeout=60)
async with ClientSession(connector=conn, auth=auth) as session:
await asyncio.gather(*[asyncio.ensure_future(self.download_and_save(session, url)) for url in urls])
async def download_and_save(self, session, url):
content_task = asyncio.ensure_future(self.fetch(session, url))
content = await content_task
# Bonus Question 2: This is blocking, I know. Should this be wrapped in another coro
# or should I use something like asyncio.as_completed in the download function?
self.data_handler.take(origin_url=url, data=content)
def download(self, urls, auth=None):
if isinstance(auth, tuple):
auth = BasicAuth(*auth)
print('Running on concurrency level {}'.format(self.concurrent_connections))
self.sending_bar = tqdm(urls, total=len(urls), desc='Sent ', unit='requests')
self.sending_bar.update(0)
self.receiving_bar = tqdm(urls, total=len(urls), desc='Reveived', unit='requests')
self.receiving_bar.update(0)
tasks = self.batch_download(urls, auth)
self.loop.run_until_complete(tasks)
return self.data_handler.done()
### call like so ###
URL_PATTERN = 'https://www.example.com/{}.html'
def gen_url(lower=0, upper=None):
for i in range(lower, upper):
yield URL_PATTERN.format(i)
ad = AsyncDownloader(concurrent_connections=30)
data = ad.download([g for g in gen_url(upper=1000)])
