asyncio/aiohttp 不返回响应

Question

我正在尝试通过使用 asyncio/aiohttp 并行化 Web 请求来从 https://www.officialcharts.com/ 中抓取一些数据。我实现了链接here 中给出的代码。

我遵循了两个不同的程序。第一个是这样的。

from bs4 import BeautifulSoup
from urllib.request import urlopen
from selenium import webdriver
import time
import pandas as pd
import numpy as np
import re
import json

import requests
from bs4 import BeautifulSoup
from datetime import date, timedelta
from IPython.display import clear_output
import memory_profiler

import spotipy
import spotipy.util as util
import pandas as pd
from  more_itertools import unique_everseen

weeks = []
d = date(1970, 1, 1) 
d += timedelta(days = 6 - d.weekday())

for i in range(2500):    
    weeks.append(d.strftime('%Y%m%d'))
    d += timedelta(days = 7)

import asyncio
from aiohttp import ClientSession
import nest_asyncio
nest_asyncio.apply()

result = []
async def fetch(url, session):
    async with session.get(url) as response:
        return await response.read()

async def run(r):  
    tasks = []

    # Fetch all responses within one Client session,
    # keep connection alive for all requests.
    async with ClientSession() as session:
        for i in range(r):
            url = 'https://www.officialcharts.com/charts/singles-chart/' + weeks[i] + '/'
            task = asyncio.ensure_future(fetch(url, session))
            tasks.append(task)

        responses = await asyncio.gather(*tasks)
        result.append(responses)


loop = asyncio.get_event_loop()
future = asyncio.ensure_future(run(5))
loop.run_until_complete(future)

print('Done')
print(result[0][0] == None)

上述代码的问题是，当我同时发出超过 1000 个请求时，它会失败。

post 的作者实施了一个不同的程序来解决这个问题，他声称我们可以处理多达 10K 的请求。我遵循了他的第二个程序，这是我的代码。

import random
import asyncio
from aiohttp import ClientSession
import nest_asyncio
nest_asyncio.apply()

result = []
async def fetch(url, session):
    async with session.get(url) as response:
        delay = response.headers.get("DELAY")
        date = response.headers.get("DATE")
        print("{}:{} with delay {}".format(date, response.url, delay))
        return await response.read()


async def bound_fetch(sem, url, session):
    # Getter function with semaphore.
    async with sem:
        await fetch(url, session)


async def run(r):
    tasks = []
    # create instance of Semaphore
    sem = asyncio.Semaphore(1000)

    # Create client session that will ensure we dont open new connection
    # per each request.
    async with ClientSession() as session:
        for i in range(r):         
            url = 'https://www.officialcharts.com/charts/singles-chart/' + weeks[i] + '/'
            task = asyncio.ensure_future(bound_fetch(sem, url, session))
            tasks.append(task)

        responses = await asyncio.gather(*tasks)
        result.append(responses)

number = 5

loop = asyncio.get_event_loop()
future = asyncio.ensure_future(run(number))
loop.run_until_complete(future)

print('Done')
print(result[0][0] == None)

由于某种原因，这不会返回任何响应。

PS：我不是CS背景，只是为了好玩而编程。我不知道异步代码中发生了什么。

Answer 1

尝试使用最新版本。

#!/usr/bin/env python3
# -*- coding: utf-8 -*-

from aiohttp import ClientSession, client_exceptions
from asyncio import Semaphore, ensure_future, gather, run
from json import dumps, loads

limit = 10
http_ok = [200]


async def scrape(url_list):
    tasks = list()
    sem = Semaphore(limit)

    async with ClientSession() as session:
        for url in url_list:
            task = ensure_future(scrape_bounded(url, sem, session))
            tasks.append(task)

        result = await gather(*tasks)

    return result


async def scrape_bounded(url, sem, session):
    async with sem:
        return await scrape_one(url, session)


async def scrape_one(url, session):
    try:
        async with session.get(url) as response:
            content = await response.read()
    except client_exceptions.ClientConnectorError:
        print('Scraping %s failed due to the connection problem', url)
        return False

    if response.status not in http_ok:
        print('Scraping%s failed due to the return code %s', url, response.status)
        return False

    content = loads(content.decode('UTF-8'))

    return content

if __name__ == '__main__':
    urls = ['http://demin.co/echo1/', 'http://demin.co/echo2/']
    res = run(scrape(urls))

    print(dumps(res, indent=4))

这是一个真实的project 的模板，按预期工作。

你可以找到这个源代码here