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python - 当条件不满足时，无法让我的脚本继续尝试几次

问题描述

我在 python 中创建了一个脚本来从网页的不同链接中获取某些帖子的标题。问题是我尝试玩的网页有时无法为我提供有效的响应，但当我尝试两次或三次时，我确实得到了有效的响应。

我一直在尝试以这种方式创建一个循环，以便脚本检查我定义的标题是否为空。如果标题什么都没有，那么脚本将继续循环 4 次以查看是否可以成功。但是，在每个链接的第四次尝试之后，脚本将去另一个链接重复相同的操作，直到所有链接都用尽。

到目前为止，这是我的尝试：

import time
import requests
from bs4 import BeautifulSoup

links = [
    "https://stackoverflow.com/questions/tagged/web-scraping?sort=newest&page=2",
    "https://stackoverflow.com/questions/tagged/web-scraping?sort=newest&page=3",
    "https://stackoverflow.com/questions/tagged/web-scraping?sort=newest&page=4"
    ]
counter = 0

def fetch_data(link):
    global counter
    res = requests.get(link)
    soup = BeautifulSoup(res.text,"lxml")
    try:
        title = soup.select_one("p.tcode").text
    except AttributeError: title = ""

    if not title:
        while counter<=4:
            time.sleep(1)
            print("trying {} times".format(counter))
            counter += 1
            fetch_data(link)
    else:
        counter = 0

    print("tried with this link:",link)

if __name__ == '__main__':
    for link in links:
        fetch_data(link)

这是我现在可以在控制台中看到的输出：

trying 0 times
trying 1 times
trying 2 times
trying 3 times
trying 4 times
tried with this link: https://stackoverflow.com/questions/tagged/web-scraping?sort=newest&page=2
tried with this link: https://stackoverflow.com/questions/tagged/web-scraping?sort=newest&page=2
tried with this link: https://stackoverflow.com/questions/tagged/web-scraping?sort=newest&page=2
tried with this link: https://stackoverflow.com/questions/tagged/web-scraping?sort=newest&page=2
tried with this link: https://stackoverflow.com/questions/tagged/web-scraping?sort=newest&page=2
tried with this link: https://stackoverflow.com/questions/tagged/web-scraping?sort=newest&page=2
tried with this link: https://stackoverflow.com/questions/tagged/web-scraping?sort=newest&page=3
tried with this link: https://stackoverflow.com/questions/tagged/web-scraping?sort=newest&page=4

我的预期输出：

trying 0 times
trying 1 times
trying 2 times
trying 3 times
trying 4 times
tried with this link: https://stackoverflow.com/questions/tagged/web-scraping?sort=newest&page=2
trying 0 times
trying 1 times
trying 2 times
trying 3 times
trying 4 times
tried with this link: https://stackoverflow.com/questions/tagged/web-scraping?sort=newest&page=3
trying 0 times
trying 1 times
trying 2 times
trying 3 times
trying 4 times
tried with this link: https://stackoverflow.com/questions/tagged/web-scraping?sort=newest&page=4

PS I used wrong selector within my script so that I can let it meet the condition I've defined above.

当不满足条件时，如何让我的脚本继续尝试每个链接几次

标签： pythonpython-3.xweb-scrapingconditional-statements

解决方案

我认为重新安排您的代码如下。

import time
import requests
from bs4 import BeautifulSoup
​
links = [
    "https://stackoverflow.com/questions/tagged/web-scraping?sort=newest&page=2",
    "https://stackoverflow.com/questions/tagged/web-scraping?sort=newest&page=3",
    "https://stackoverflow.com/questions/tagged/web-scraping?sort=newest&page=4"
    ]

def fetch_data(link):
    global counter
    res = requests.get(link)
    soup = BeautifulSoup(res.text,"lxml")
    try:
        title = soup.select_one("p.tcode").text
    except AttributeError: title = ""
​
    if not title:
        while counter<=4:
            time.sleep(1)
            print("trying {} times".format(counter))
            counter += 1
            fetch_data(link)   
​
if __name__ == '__main__':
    for link in links:
        counter = 0
        fetch_data(link)
        print("tried with this link:",link)

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