我正在尝试为学术目的构建蜘蛛/网络爬虫,以从学术出版物中获取文本并将相关链接附加到URL堆栈.我正在尝试抓取1个名为“ PubMed”的网站.我似乎无法抓住我需要的链接.这是我的带有示例页面的代码,此页面应代表他们数据库中的其他人：

 website = 'http://www.ncbi.nlm.nih.gov/pubmed/?term=mtap+prmt'
 from bs4 import BeautifulSoup
 import requests
 r = requests.get(website)
 soup = BeautifulSoup(r.content)

我已将html树分解成几个变量,以提高可读性,以便它们都适合1个屏幕宽度.

 key_text = soup.find('div', {'class':'grid'}).find('div',{'class':'col twelve_col nomargin shadow'}).find('form',{'id':'EntrezForm'})
 side_column = key_text.find('div', {'xmlns:xi':'http://www.w3.org/2001/XInclude'}).find('div', {'class':'supplemental col three_col last'})
 side_links = side_column.find('div').findAll('div')[1].find('div', {'id':'disc_col'}).findAll('div')[1]

 for link in side_links:
      print link

如果您使用chrome inspect元素查看html源代码,则应该在“ side_links”中包含链接的其他多个嵌套div.但是,上面的代码产生以下错误：

 Traceback (most recent call last):
 File "C:/Users/ballbag/Copy/web_scraping/google_search.py", line 22, in <module>
 side_links = side_column.find('div').findAll('div')[1].find('div',      {'id':'disc_col'}).findAll('div')[1]
 IndexError: list index out of range

如果您转到网址,则右侧会显示一列“相关链接”,其中包含我要抓取的网址.但是我似乎无法找到他们.有一个声明说我正在尝试进入div,我怀疑这与它有关.任何人都可以帮助抓住这些链接吗？我真的很感激任何指针

解决方法:

问题是侧栏加载了其他异步请求.

这里的想法是：

>使用requests.Session维护网络抓取会话
>解析用于获取侧栏的网址
>跟随该链接,并从div获得class =“ portlet_content”的链接.

码：

from urlparse import urljoin

from bs4 import BeautifulSoup
import requests


base_url = 'http://www.ncbi.nlm.nih.gov'
website = 'http://www.ncbi.nlm.nih.gov/pubmed/?term=mtap+prmt'

# parse the main page and grab the link to the side bar
session = requests.Session()
soup = BeautifulSoup(session.get(website).content)

url = urljoin(base_url, soup.select('div#disc_col a.disc_col_ph')[0]['href'])

# parsing the side bar
soup = BeautifulSoup(session.get(url).content)

for a in soup.select('div.portlet_content ul li.brieflinkpopper a'):
    print a.text, urljoin(base_url, a.get('href'))

印刷品：

The metabolite 5'-methylthioadenosine signals through the adenosine receptor A2B in melanoma. http://www.ncbi.nlm.nih.gov/pubmed/25087184
Down-regulation of methylthioadenosine phosphorylase (MTAP) induces progression of hepatocellular carcinoma via accumulation of 5'-deoxy-5'-methylthioadenosine (MTA). http://www.ncbi.nlm.nih.gov/pubmed/21356366
Quantitative analysis of 5'-deoxy-5'-methylthioadenosine in melanoma cells by liquid chromatography-stable isotope ratio tandem mass spectrometry. http://www.ncbi.nlm.nih.gov/pubmed/18996776
...
Cited in PMC http://www.ncbi.nlm.nih.gov/pmc/articles/pmid/23265702/citedby/?tool=pubmed