The website is API（2）

一、Beautifu Soup库

from bs4 import BeautifulSoup
soup = BeautifulSoup(demo,"html.parser")

Tag、Name、Attributes、NavigableString、Comment

.contents 子节点的列表，将<tag>所有儿子节点存入列表

.children 子节点的迭代类型

.descendants 子孙节点的迭代类型

.parent 节点的父亲标签

.parents 节点先辈标签的迭代类型

 .next_sibling(s) 返回安照HTML文本顺序的下一个平行节点标签

.previous_sibling(s) 上一个

>>> import requests
>>> r = requests.get("http://python123.io/ws/demo.html")
>>> demo = r.text
>>> demo
'<html><head><title>This is a python demo page</title></head>
<body>
<p class="title"><b>The demo python introduces several python courses.</b></p>
<p class="course">Python is a wonderful general-purpose programming language. You can learn Python from novice to professional by tracking the following courses:
<a href="http://www.icourse163.org/course/BIT-268001" class="py1" id="link1">Basic Python</a> and <a href="http://www.icourse163.org/course/BIT-1001870001" class="py2" id="link2">Advanced Python</a>.</p>
</body></html>'
>>>from bs4 import BeautifulSoup

>>> soup = BeautifulSoup(demo,"html.parser")
>>> soup.prettify()
'<html> <head> <title> This is a python demo page </title> </head> <body> <p class="title"> <b> The demo python introduces several python courses. </b> </p> <p class="course"> Python is a wonderful general-purpose programming language. You can learn Python from novice to professional by tracking the following courses: <a class="py1" href="http://www.icourse163.org/course/BIT-268001" id="link1"> Basic Python </a> and <a class="py2" href="http://www.icourse163.org/course/BIT-1001870001" id="link2"> Advanced Python </a> . </p> </body> </html>'
>>> print(soup.prettify())
<html>
<head>
<title>
This is a python demo page
</title>
</head>
<body>
<p class="title">
<b>
The demo python introduces several python courses.
</b>
</p>
<p class="course">
Python is a wonderful general-purpose programming language. You can learn Python from novice to professional by tracking the following courses:
<a class="py1" href="http://www.icourse163.org/course/BIT-268001" id="link1">
Basic Python
</a>
and
<a class="py2" href="http://www.icourse163.org/course/BIT-1001870001" id="link2">
Advanced Python
</a>
.
</p>
</body>
</html>

二、信息组织与提取 

1.信息标记的三种形式：

XML：尖括号

JSON：有类型键值对

YAML：无类型

3.信息提取的一般方法

（1）完整解析信息地标记形式，再提取关键信息

（2）无视标记形式，直接搜索关键信息

（3）融合方法

实例：

>>>  import requests
 r = requests.get("http://python123.io/ws/demo.html")
 demo = r.text
 demo
 
SyntaxError: unexpected indent
>>> import requests
>>> r = requests.get("http://python123.io/ws/demo.html")
>>> demo = r.text
>>> demo
'<html><head><title>This is a python demo page</title></head>
<body>
<p class="title"><b>The demo python introduces several python courses.</b></p>
<p class="course">Python is a wonderful general-purpose programming language. You can learn Python from novice to professional by tracking the following courses:
<a href="http://www.icourse163.org/course/BIT-268001" class="py1" id="link1">Basic Python</a> and <a href="http://www.icourse163.org/course/BIT-1001870001" class="py2" id="link2">Advanced Python</a>.</p>
</body></html>'
>>> from bs4 import BeautifulSoup
>>> soup = BeautifulSoup(demo,"html,parser")
Traceback (most recent call last):
  File "<pyshell#6>", line 1, in <module>
    soup = BeautifulSoup(demo,"html,parser")
  File "C:UsersASUSAppDataLocalProgramsPythonPython37-32libsite-packagess4\__init__.py", line 196, in __init__
    % ",".join(features))
bs4.FeatureNotFound: Couldn't find a tree builder with the features you requested: html,parser. Do you need to install a parser library?
>>> yes
Traceback (most recent call last):
  File "<pyshell#7>", line 1, in <module>
    yes
NameError: name 'yes' is not defined
>>> soup = BeautifulSoup(demo,"html.parser")
>>> from link in soup.find_all('a')
SyntaxError: invalid syntax
>>> for link in soup.find_all('a')
SyntaxError: invalid syntax
>>> for link in soup.find_all('a'):
    print(link.get('href'))

    
http://www.icourse163.org/course/BIT-268001
http://www.icourse163.org/course/BIT-1001870001

4.基于bs4库的HTML内容查找方法

<>.find_all(name,attrs,recursive,string,**kwargs)

返回一个列表类型，存储查找的结果

name：对标签名称的检索字符串

>>> soup.find_all('a')
[<a class="py1" href="http://www.icourse163.org/course/BIT-268001" id="link1">Basic Python</a>, <a class="py2" href="http://www.icourse163.org/course/BIT-1001870001" id="link2">Advanced Python</a>]
>>> soup.find_all(['a','b'])
[<b>The demo python introduces several python courses.</b>, <a class="py1" href="http://www.icourse163.org/course/BIT-268001" id="link1">Basic Python</a>, <a class="py2" href="http://www.icourse163.org/course/BIT-1001870001" id="link2">Advanced Python</a>]
>>> for tag in soup.find_all(True):
    print(tag.name)

    
html
head
title
body
p
b
p
a
a
>>> import re
>>> for tag in soup.find_all(re.compile('b')):
    print(tag.name)

    
body
b

attrs：对标签属性值的检索字符串，可标注属性检索

>>> soup.find_all('p','course')
[<p class="course">Python is a wonderful general-purpose programming language. You can learn Python from novice to professional by tracking the following courses:

<a class="py1" href="http://www.icourse163.org/course/BIT-268001" id="link1">Basic Python</a> and <a class="py2" href="http://www.icourse163.org/course/BIT-1001870001" id="link2">Advanced Python</a>.</p>]
>>> soup.find_all(id='link1')
[<a class="py1" href="http://www.icourse163.org/course/BIT-268001" id="link1">Basic Python</a>]
>>> soup.find_all(id=re.compile('link'))
[<a class="py1" href="http://www.icourse163.org/course/BIT-268001" id="link1">Basic Python</a>, <a class="py2" href="http://www.icourse163.org/course/BIT-1001870001" id="link2">Advanced Python</a>]

recursive：是否对子孙全部检索，默认True

>>> soup.find_all('a',recursive=False)
[]

string：<>...</>中字符串区域的检索字符串

>>> soup.find_all(string = 'Basic Python')
['Basic Python']
>>> soup.find_all(string = re.compile("python"))
['This is a python demo page', 'The demo python introduces several python courses.']

>>> soup(string = 'Basic Python')
['Basic Python']

扩展方法：

<>.find() find_parents parent next_sibling(s) previous_sibling(s)

三、中国大学排名定向爬虫

技术路线：requests+bs4

可行性：robots协议

步骤1：获取内容 getHTMLText()

2：数据结构 fillUnivList()

3：利用DS printUnivList()

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):#过滤
            tds = tr('td')
            ulist.append([tds[0].string,tds[1].string,tds[3].string])

def printUnivList(ulist,num):
    #tplt = "{0:^10}	{1:{3}^10}	{2:^10}"
    print("{:^10}	{:^6}	{:^10}".format("排名","学校名称","总分"))
    for i in range(num):
        u = ulist[i]
        print("{:^10}	{:^6}	{:^10}".format(u[0],u[1],u[2]))
        

def main():
    uinfo = []
    url='http://www.zuihaodaxue.com/zuihaodaxuepaiming2019.html'
    html = getHTMLText(url)
    fillUnivList(uinfo,html)
    printUnivList(uinfo,20)
main()

优化后：

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):#过滤
            tds = tr('td')
            ulist.append([tds[0].string,tds[1].string,tds[3].string])

def printUnivList(ulist,num):
    tplt = "{0:^10}	{1:{3}^10}	{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.com/zuihaodaxuepaiming2019.html'
    html = getHTMLText(url)
    fillUnivList(uinfo,html)
    printUnivList(uinfo,20)
main()
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原文地址：https://www.cnblogs.com/kmxojer/p/11436741.html