Python爬虫入门——爬取中国大学排名

中国大学排名相关链接：​​http://www.zuihaodaxue.cn/zuihaodaxuepaiming2016.html​​

分析源代码得：大学排名的数据都存储于tbody标签下的子标签（关键）

import requests
from bs4 import BeautifulSoup
import bs4

def getHTMLText(url):
    try:
        r = requests.get(url, timeout=30)
        r.raise_for_status()
        r.encoding = r.apparent_encoding
        return r.text
    except:
        return ""

def fillUnivList(ulist, html):
    soup = BeautifulSoup(html, 'html.parser')
    for tr in soup.find('tbody').children:
        if isinstance(tr, bs4.element.Tag):
            tds = tr('td')
            ulist.append([tds[0].string, tds[1].string, tds[3].string])

def printUnivList(ulist, num):
    tplt = "{0:^10}\t{1:{3}^10}\t{2:^10}"
    print(tplt.format("排名", "学校名称", "总分", chr(12288)))
    for i in range(num):
        u=ulist[i]
        print(tplt.format(u[0],u[1],u[2],chr(12288)))

def main():
    uinfo = []
    url = "http://www.zuihaodaxue.cn/zuihaodaxuepaiming2016.html"
    html = getHTMLText(url)
    fillUnivList(uinfo,html)
    printUnivList(uinfo,20) #二十所学校的排名
main()

1-  getHTMLText(url)

def getHTMLText(url):
    try:
        r = requests.get(url, timeout=30)
        r.raise_for_status()
        r.encoding = r.apparent_encoding
        return r.text
    except:
        return ""

调用requests库 抓取对应网页的内容若正常 则返回网页的代码,否者返回空

2-  fillUnivList(ulist, html)

def fillUnivList(ulist, html):
    soup = BeautifulSoup(html, 'html.parser')
    for tr in soup.find('tbody').children:
        if isinstance(tr, bs4.element.Tag):
            tds = tr('td')
            ulist.append([tds[0].string, tds[1].string, tds[3].string])

调用BeautifulSoup库 整理数据 观察网页源代码可知

数据都存储在tbody标签的子标签td中

用isinstance()方法 检查tbody的子标签是否为 bs4.element.Tag类

并将筛选过的数据通过嵌套的列表保存起来

tds[0]存储排名 tds[1]存储学校名称 tds[2]存储地名 tds[3]存储总分

我们只需要 排名,学校名称,总分 故只将tds[0],tds[1],tds[3]存储为新列表即可

3-  printUnivList(ulist, num)

def printUnivList(ulist, num):
    tplt = "{0:^10}\t{1:{3}^10}\t{2:^10}"
    print(tplt.format("排名", "学校名称", "总分", chr(12288)))
    for i in range(num):
        u=ulist[i]
        print(tplt.format(u[0],u[1],u[2],chr(12288)))

注意中英文对齐布局问题

chr(12288)是utf-8中 中文空格的编号

大意:间隔全用中文空格就可以避免布局不整齐的问题

Last

通过主函数调用就可以爬取到中国大学的排名了

 问题小结

错误代码1

import requests
from bs4 import BeautifulSoup
import bs4

def getHTMLText(url):
    try:
        r = requests.get(url, timeout=30)
        r.raise_for_status()
        r.encoding = r.apparent_encoding
        return r.text
    except:
        return ""

def fillUnivList(ulist, html):
    soup = BeautifulSoup(html, 'html.parser')
    for tr in soup.find('tbody').children:
        if isinstance(tr, bs4.element.Tag):
            tds = tr('td')
            ulist.append([tds[0].string, tds[1].string, tds[3].string])

def printUnivList(ulist, num):
    tplt = "{0:^10}\t{1:{3}^10}\t{2:^10}"
    print(tplt.format("排名", "学校名称", "总分", chr(12288)))
    for i in range(num):
        u=ulist[i]
        print(tplt.format(u[0],u[1],u[2],chr(12288)))

def main():
    uinfo = []
    url = "http://www.zuihaodaxue.cn/zuihaodaxuepaiing2016.html"
    html = getHTMLText(url)
    fillUnivList(uinfo,html)
    printUnivList(uinfo,20) #二十所学校的排名
main()

for tr in soup.find('tbody').children:

在这里出现了traceback

发生异常: AttributeError

'NoneType' object has no attribute 'children'

错误代码1：我的网站打错了 更改以后就可以了

错误代码2

import requests
from bs4 import BeautifulSoup
import bs4

def getHTMLText(url):
    try:
        r = requests.get(url, timeout=30)
        r.raise_for_status()
        r.encoding = r.apparent_encoding
        return r.text
    except:
        return ""

def fillUnivList(ulist, html):
    soup = BeautifulSoup(html, 'html.parser')
    for tr in soup.find('tbody').children:
        if isinstance(tr, bs4.element.Tag):
            tds = tr('td')
            ulist.append([tds[0].string, tds[1].string, tds[3].string)

def printUnivList(ulist, num):
    tplt = "{0:^10}\t{1:{3}^10}\t{2:^10}"
    print(tplt.format("排名", "学校名称", "总分", chr(12288)))
    for i in range(num):
        u=ulist[i]
        print(tplt.format(u[0],u[1],u[2],chr(12288)))

def main():
    uinfo = []
    url = "http://www.zuihaodaxue.cn/zuihaodaxuepaiming2016.html"
    html = getHTMLText(url)
    fillUnivList(uinfo,html)
    printUnivList(uinfo,20) #二十所学校的排名
main()

 这段代码在vscode的显示：

错误代码2：fillUnivList(ulist,html)函数的最后一个tds后少打了一个方括号

总结下来就是打错字了