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>\r\n<body>\r\n<p class="title"><b>The demo python introduces several python courses.</b></p>\r\n<p class="course">Python is a wonderful general-purpose programming language. You can learn Python from novice to professional by tracking the following courses:\r\n<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>\r\n</body></html>'

>>>from bs4 import BeautifulSoup

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


The demo python introduces several python courses.



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>
.

</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>\r\n<body>\r\n<p class="title"><b>The demo python introduces several python courses.</b></p>\r\n<p class="course">Python is a wonderful general-purpose programming language. You can learn Python from novice to professional by tracking the following courses:\r\n<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>\r\n</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:\Users\ASUS\AppData\Local\Programs\Python\Python37-32\lib\site-packages\bs4\__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}\t{1:{3}^10}\t{2:^10}"

    print("{:^10}\t{:^6}\t{:^10}".format("排名","学校名称","总分"))

    for i in range(num):

        u = ulist[i]

        print("{:^10}\t{:^6}\t{:^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}\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.com/zuihaodaxuepaiming2019.html'

    html = getHTMLText(url)

    fillUnivList(uinfo,html)

    printUnivList(uinfo,20)

main()

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The website is API（2）

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