BeautifulSoup4 抓取无法超出网站的第一页（Python 3.6）

Question

我正在尝试从本网站的第一页到第 14 页：https://cross-currents.berkeley.edu/archives?author=&title=&type=All&issue=All&region=All 这是我的代码：

import requests as r
from bs4 import BeautifulSoup as soup
import pandas 

#make a list of all web pages' urls
webpages=[]
for i in range(15):
    root_url = 'https://cross-currents.berkeley.edu/archives?author=&title=&type=All&issue=All&region=All&page='+ str(i)
    webpages.append(root_url)
    print(webpages)

#start looping through all pages
for item in webpages:  
    headers = {'User-Agent': 'Mozilla/5.0'}
    data = r.get(item, headers=headers)
    page_soup = soup(data.text, 'html.parser')

#find targeted info and put them into a list to be exported to a csv file via pandas
    title_list = [title.text for title in page_soup.find_all('div', {'class':'field field-name-node-title'})]
    title = [el.replace('\n', '') for el in title_list]

#export to csv file via pandas
    dataset = {'Title': title}
    df = pandas.DataFrame(dataset)
    df.index.name = 'ArticleID'
    df.to_csv('example31.csv',encoding="utf-8")

输出的 csv 文件只包含最后一页的目标信息。当我打印“网页”时，它表明所有页面的 url 都已正确放入列表中。我究竟做错了什么？提前谢谢！

Answer 1

您只是为所有页面覆盖相同的输出 CSV 文件，您可以在“附加”模式下调用 .to_csv() 以将新数据添加到现有文件的末尾：

df.to_csv('example31.csv', mode='a', encoding="utf-8", header=False)

或者，更好的办法是将标题收集到标题列表中，然后转储到 CSV 中一次：

#start looping through all pages
titles = []
for item in webpages:
    headers = {'User-Agent': 'Mozilla/5.0'}
    data = r.get(item, headers=headers)
    page_soup = soup(data.text, 'html.parser')

    #find targeted info and put them into a list to be exported to a csv file via pandas
    title_list = [title.text for title in page_soup.find_all('div', {'class':'field field-name-node-title'})]

    titles += [el.replace('\n', '') for el in title_list]

# export to csv file via pandas
dataset = [{'Title': title} for title in titles]
df = pandas.DataFrame(dataset)
df.index.name = 'ArticleID'
df.to_csv('example31.csv', encoding="utf-8")

Answer 2

除了 alexce 发布的内容之外，另一种方法是继续将内部的数据帧附加到新的数据帧，然后将其写入 CSV。

将 finalDf 声明为循环外的数据框：

finalDf = pandas.DataFrame()

稍后再做：

for item in webpages:
    headers = {'User-Agent': 'Mozilla/5.0'}
    data = r.get(item, headers=headers)
    page_soup = soup(data.text, 'html.parser')

#find targeted info and put them into lists to be exported to a csv file   via pandas
    title_list = [title.text for title in page_soup.find_all('div', {'class':'field field-name-node-title'})]
    title = [el.replace('\n', '') for el in title_list]

#export to csv file via pandas
    dataset = {'Title': title}
    df = pandas.DataFrame(dataset)
    finalDf = finalDf.append(df)
    #df.index.name = 'ArticleID'
    #df.to_csv('example31.csv', mode='a', encoding="utf-8", header=False)

finalDf = finalDf.reset_index(drop = True)
finalDf.index.name = 'ArticleID'
finalDf.to_csv('example31.csv', encoding="utf-8")

注意带有finalDf的行