示例网站：https://python123.io/ws/demo....
>>> import requests
>>> r = requests.get('https://python123.io/ws/demo.html')
>>> r.text
'<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>'
>>> demo = r.text
>>> from bs4 import BeautifulSoup
>>> soup = BeautifulSoup(demo,'html.parser')
>>> 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>我们使用soup的prettify方法来漂亮打印HTML页面。
BeautifulSoup库的基本元素
html元素的介绍：
<p class="title">
<b>
The demo python introduces several python courses.
</b>
</p>在以上的代码中，<p>..</p> 就是标签，Tag；
标签的名字name 就是 p
class 就是属性（Attributes），属性是由键值对构成的。
beautifulsoup类就是对应着HTML页面。
BeautifulSoup 库解析器
无论哪种解析器都可以处理HTML文档的
| 解析器 | 使用方法 | 条件 |
|---|---|---|
| bs4的HTML解析器 | BeautifulSoup（mk,'html.parser'） |
安装bs4库 |
| lxml的HTML解析器 | BeautifulSoup（mk,'lxml'） |
pip install lxml |
| lxml的XML解析器 | BeautifulSoup（mk,'xml'） |
pip install lxml |
| html5lib解析器 | BeautifulSoup（mk,'html5lib'） |
pip install html5lib |
BeautifulSoup 类的基本元素
| 基本元素 | 说明 |
|---|---|
| Tag | 标签，最基本的信息组织单元，分别用<>和</>表明开头和结尾 |
| Name | 标签的名字，<p>..</p>的名字是‘p’，格式：<tag>.name |
| Attributes | 标签的属性，字典形式组织，格式：<tag>.attrs |
| NavigableString | 标签内非属性字符串，<>..</>中字符串，格式：<tag>.string |
| Comment | 标签内字符串的注释部分，一种特殊的Comment类型 |
>>> tag = soup.a
>>> tag
<a class="py1" href="http://www.icourse163.org/course/BIT-268001" id="link1">Basic Python</a>soup中所有的标签都可以使用soup.tag的形式访问，当文档中存在多个同名标签，则只访问第一个。
访问标签名字的方法：
>>> tag.name
'a'
>>> tag.parent.name
'p'
>>> tag.parent.parent.name
'body'访问标签属性的方法，无论标签是否存在属性，都会返回一个字典。
>>> tag.attrs
{'href': 'http://www.icourse163.org/course/BIT-268001', 'class': ['py1'], 'id': 'link1'}
>>> tag.attrs['href']
'http://www.icourse163.org/course/BIT-268001'
>>> tag.attrs['class']
['py1']
>>> type(tag.attrs)
<class 'dict'>
>>> type(tag)
<class 'bs4.element.Tag'>#标签是标签属性访问NavigableString的方法：
>>> tag.string
'Basic Python'
>>> soup.p
<p class="title"><b>The demo python introduces several python courses.</b></p>
>>> soup.p.string
'The demo python introduces several python courses.'
>>> type(soup.p.string)
<class 'bs4.element.NavigableString'>#这个字符串不是普通字符串类型访问Comment注释的方法
>>> newsoup = BeautifulSoup("<b><!--This is a comment--></b><p>This is not a comment</p>",'html.parser')
>>> newsoup.b.string
'This is a comment'
>>> type(newsoup.b.string)
<class 'bs4.element.Comment'>
>>> newsoup.p.string
'This is not a comment'
>>> type(newsoup.p.string)
<class 'bs4.element.NavigableString'>若分析文本时不需要注释的内容，用类型来判断一下就可以过滤掉注释的内容。
HTML遍历方法：
1.从根节点向叶子节点下行遍历
2.从叶子节点向根节点上行遍历
3.从叶子节点到叶子节点的平行遍历方式
下行遍历方法：
| 属性 | 说明 |
|---|---|
| .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，与.contents类似，用于循环遍历儿子节点 |
| .descendants | 子孙节点的迭代类型，包含所有子孙节点，用于循环遍历 |
>>> soup.body
<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>
>>> soup.body.contents
['\n', <p class="title"><b>The demo python introduces several python courses.</b></p>, '\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:
<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>, '\n']
>>> len(soup.body.contents)
5
>>> for child in soup.body.children:
print(child)
<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>
>>> for child in soup.body.descendants:
print(child)
<p class="title"><b>The demo python introduces several python courses.</b></p>
<b>The demo python introduces several python courses.</b>
The demo python introduces several python courses.
<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>
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>
Basic Python
and
<a class="py2" href="http://www.icourse163.org/course/BIT-1001870001" id="link2">Advanced Python</a>
Advanced Python
.上行遍历方法
| 属性 | 说明 |
|---|---|
| .parent | 节点的父亲标签 |
| .parents | 节点先辈标签的迭代类型，用于循环遍历先辈节点 |
>>> soup.title.parent
<head><title>This is a python demo page</title></head>
>>> soup.html.parent
<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>
>>> soup.parent
>>> for parent in soup.a.parents:
if parent is None:
print(parent)
else:
print(parent.name)
p
body
html
[document]标签树的平行遍历
| 属性 | 说明 |
|---|---|
| .next_sibling | 返回按照HTML文本顺序的下一个平行节点标签 |
| .previous_sibling | 返回按照HTML文本顺序的上一个平行节点标签 |
| .next_siblings | 迭代类型，返回按照HTML文本顺序的后续所有平行节点标签 |
| .previous_siblings | 迭代类型，返回按照HTML文本顺序的前续所有平行节点标签 |
重要：平行遍历发送在同一个父亲节点下的各个节点之间
>>> soup.a.next_sibling
' and '
>>> soup.a.next_sibling.next_sibling
<a class="py2" href="http://www.icourse163.org/course/BIT-1001870001" id="link2">Advanced Python</a>
>>> soup.a.previous_sibling
'Python is a wonderful general-purpose programming language. You can learn Python from novice to professional by tracking the following courses:\r\n'
>>> soup.a.previous_sibling.previous_siblingbs4的html页面友好输出：
print(soup.prettify())XML：扩展标记语言 与HTML格式类似。最早的通用信息标记语言，可扩展性好，但繁琐。主要采用
JSON:JS语言中面向对象的一种信息标记形式
JSON是有类型的键值对 key:value。信息有类型，适合程序处理（js），较XML简洁。主要用于节点通信，不能注释
YAML:无类型键值对 key:value 。信息无类型，文本信息比例最高，可读性好。各类系统的配置文件，有注释易读
文本解析的基本思路
>>> for link in soup.find_all('a'):
print(link.get('href'))
http://www.icourse163.org/course/BIT-268001
http://www.icourse163.org/course/BIT-1001870001soup.find_all()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')[0]
<a class="py1" href="http://www.icourse163.org/course/BIT-268001" id="link1">Basic Python</a>
>>> soup.find_all(['a','b'])#同时搜索两个参数需要传入一个列表
[<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现在要搜索所有以‘b’开头的标签，包括和<body>标签。
attrs:对标签属性值的检索字符串，可标注属性检索
recursive:是否对子孙全部检索，默认True
string:对<>...</>中字符串区域的检索字符串
<tag>(..)等价于 <tag>.find_all(..)
soup(..)等价于 soup.find_all(..)
实例：中国大学排名的爬虫实现
URL链接为：http://www.zuihaodaxue.com/zu...
首先确定我们想获得的信息是否在HTML页面中，而不是用js形成的。
在这里，我们在HTML页面中看到了全部信息，那么现在对程序结构进行一下初步设计。
步骤1：从网络上获取大学排名网页内容，getHTMLText()
步骤2：提取网页内容中信息到合适的数据结构,fillUnivList()（关键点）
步骤3：利用数据结构展示并输出结构,printUnivList()
import requests
from bs4 import BeautifulSoup as bs
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:
print('爬取网页失败')
def fillUnivList(ulist,html):
soup = bs(html,'html.parser')
for tr in soup.find('tbody').children:
if isinstance(tr,bs4.element.Tag):#过滤掉非标签内容,必须引入bs4库
tds = tr('td') #tr.find_all('td'),查找所有td标签
ulist.append([tds[0].string,tds[1].string,tds[2].string])
def printUnivList(ulist,num):
geshi = "{:^10}\t{:^6}\t{:^10}"
print(geshi.format('排名','学校名称','省市'))
for i in range(num):
u = ulist[i]
print(geshi.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) #打印前20所大学
main()
python
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