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首页 > 解决方案 > Python 仅提取 for 循环中每第 n 次出现的第一个 href 链接

html - Python 仅提取 for 循环中每第 n 次出现的第一个 href 链接

问题描述

我正在尝试使用 python 进行简单的网络抓取，但是在获取链接名称时存在问题，因为在下面提到href的同一类中有 2 到 3 个标头，而我只需要为循环中的每个新事件打印第一个标头。btn

#!/usr/bin/python3
from bs4 import BeautifulSoup
import requests

url = "https://www.learndatasci.com/free-data-science-books/"

# Getting the webpage, creating a Response object.
response = requests.get(url)

# Extracting the source code of the page.
data = response.text

# Passing the source code to BeautifulSoup to create a BeautifulSoup object for it.
soup = BeautifulSoup(data, 'lxml')

# Extracting all the <a> tags into a list.
tags = soup.find_all('a', class_='btn')

# Extracting URLs from the attribute href in the <a> tags.
for tag in tags:
    print(tag.get('href'))

上述代码的输出：

http://www.cin.ufpe.br/~tfl2/artificial-intelligence-modern-approach.9780131038059.25368.pdf
http://www.amazon.com/gp/product/0136042597/ref=as_li_tl?ie=UTF8&camp=1789&creative=9325&creativeASIN=0136042597&linkCode=as2&tag=learnds-20&linkId=3FRORB7P56CEWSK5
http://www.iro.umontreal.ca/~bengioy/papers/ftml_book.pdf
http://amzn.to/1WePh0N
http://www.e-booksdirectory.com/details.php?ebook=9575
http://amzn.to/1FcalRp

虽然需要输出：

http://www.cin.ufpe.br/~tfl2/artificial-intelligence-modern-approach.9780131038059.25368.pdf
http://www.iro.umontreal.ca/~bengioy/papers/ftml_book.pdf
http://www.e-booksdirectory.com/details.php?ebook=9575

标签： htmlpython-3.xweb-scrapingbeautifulsoup

解决方案

BeautifulSoup 具有出色的CSS 支持，只需使用它来挑选每个奇怪的项目：

soup = BeautifulSoup(data, 'lxml')
for tag in soup.select('a.btn:nth-of-type(odd)'):

演示：

>>> for tag in soup.select('a.btn:nth-of-type(odd)'): print(tag['href'])
...
http://www.cin.ufpe.br/~tfl2/artificial-intelligence-modern-approach.9780131038059.25368.pdf
http://www.iro.umontreal.ca/~bengioy/papers/ftml_book.pdf
http://www.e-booksdirectory.com/details.php?ebook=9575
... etc

<div class="book">您可以使用的每组链接都有一个父元素：

for tag in soup.select('.book a.btn:first-of-type'):

这适用于每本书的任意数量的链接。

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