Python爬虫第5课 BeautifulSoup用法详解
BeautifulSoup
BeautifulSoup是一个灵活又方便的网页解析库，处理高效，支持多种解析器。利用它不用编写正则表达式即可方便的实现网页信息的提取。
01.BeautifulSoup的安装
安装方式：pip3 install beautifulsoup4
还有不会安装的请看下方博文：
beautifulsoup安装教程
02.BeautifulSoup详解
2.1 解析库
| 解析器 | 使用方法 | 优势 | 劣势 |
|---|---|---|---|
| Python标准库 | BeautifulSoup(markup, “html.parser”) | Python的内置标准库、执行速度适中、文档容错能力强 | Python2.7.3或3.2.2前的版本中文容错能力差 |
| lxml HTML解析器 | BeautifulSoup(markup,“lxml”) | 速度快、文档容错力强 | 需要安装C语言库 |
| lxml XML解析器 | BeautifulSoup(markup,“xml”) | 速度快、唯一支持xml的解析器 | 需要安装C语言库 |
| html5lib | BeautifulSoup(markup,“html5lib”) | 最好的容错性、以浏览器的方式解析文档、生成HTML5格式的文档 | 速度慢、不依赖外部扩展 |
基本使用
from bs4 import BeautifulSoup
html = '''
The Dormouse's story
The Dormouse's story
Once upon a time there were three little sisters; and their names were
Elsie,
Lacie and
Tillie;
and they lived at the bottom of a well.
...
'''
soup = BeautifulSoup(html, 'lxml')
# 用来格式化代码，自动补全不完整的HTML代码
print(soup.prettify())
# 获取title标签
print(soup.title)
# title标签的名字
print(soup.title.name)
# title标签的内容
print(soup.title.string)
2.2 标签选择器
（1）选择元素
from bs4 import BeautifulSoup
html = '''
The Dormouse's story
The Dormouse's story
Once upon a time there were three little sisters; and their names were
Elsie,
Lacie and
Tillie;
and they lived at the bottom of a well.
...
'''
# 声明soup对象
soup = BeautifulSoup(html, 'lxml')
# 获取title标签
print(soup.title)
# title标签类型
print(type(soup.title))
# 获取head标签
print(soup.head)
# 获取p标签，只输出第一个匹配结果
print(soup.p)
（2）获取名称
from bs4 import BeautifulSoup
html = '''
The Dormouse's story
The Dormouse's story
Once upon a time there were three little sisters; and their names were
Elsie,
Lacie and
Tillie;
and they lived at the bottom of a well.
...
'''
# 声明soup对象
soup = BeautifulSoup(html, 'lxml')
# 获取名称
print(soup.title.name)
（3）获取属性
from bs4 import BeautifulSoup
html = '''
The Dormouse's story
The Dormouse's story
Once upon a time there were three little sisters; and their names were
Elsie,
Lacie and
Tillie;
and they lived at the bottom of a well.
...
'''
# 声明soup对象
soup = BeautifulSoup(html, 'lxml')
# 获取属性1
print(soup.p.attrs['name'])
# 获取属性2
print(soup.p['name'])
（4）获取内容
from bs4 import BeautifulSoup
html = '''
The Dormouse's story
The Dormouse's story
Once upon a time there were three little sisters; and their names were
Elsie,
Lacie and
Tillie;
and they lived at the bottom of a well.
...
'''
# 声明soup对象
soup = BeautifulSoup(html, 'lxml')
# 获取内容:获取p标签的内容，第一个匹配到的
print(soup.p.string)
（5）嵌套选择
from bs4 import BeautifulSoup
html = '''
The Dormouse's story
The Dormouse's story
Once upon a time there were three little sisters; and their names were
Elsie,
Lacie and
Tillie;
and they lived at the bottom of a well.
...
'''
# 声明soup对象
soup = BeautifulSoup(html, 'lxml')
# 嵌套选择:获取head标签内的title标签的内容
print(soup.head.title.string)
（6）子节点和子孙节点
from bs4 import BeautifulSoup
html = """
The Dormouse's story
Once upon a time there were three little sisters; and their names were
Elsie
Lacie
and
Tillie
and they lived at the bottom of a well.
...
"""
soup = BeautifulSoup(html,'lxml')
# 获得p标签的所有子节点，以列表的方式输出
print(soup.p.contents)
# children 也可以返回子节点，与contents不同的是它相当于一个迭代器
print(soup.p.children)
for i, child in enumerate(soup.p.children):
print(i, child)
# 获取子孙节点descendants
print(soup.p.descendants)
for i, child in enumerate(soup.p.descendants):
print(i, child)
（7）父节点和祖先节点
from bs4 import BeautifulSoup
html = """
The Dormouse's story
Once upon a time there were three little sisters; and their names were
Elsie
Lacie
and
Tillie
and they lived at the bottom of a well.
...
"""
soup = BeautifulSoup(html,'lxml')
# 获取a标签(第一个a标签)的所有父节点
# print(soup.a.parent)
# 获取a标签所有祖先节点
print(list(enumerate(soup.a.parents)))
（8）兄弟节点
from bs4 import BeautifulSoup
html = """
The Dormouse's story
Once upon a time there were three little sisters; and their names were
Elsie
Lacie
and
Tillie
and they lived at the bottom of a well.
...
"""
soup = BeautifulSoup(html,'lxml')
# 获取a标签(第一个a标签)的所有后面的兄弟节点
print(list(enumerate(soup.a.next_siblings)))
# 获取a标签(第一个a标签)的所有前面的兄弟节点
print(list(enumerate(soup.a.previous_siblings)))
2.3 标准选择器
1、find_all(name, attrs, recursive, text, **kwargs)
可根据标签名、属性、内容查找文档，返回所有元素
name属性
html='''
Hello
- Foo
- Bar
- Jay
- Foo
- Bar
'''
from bs4 import BeautifulSoup
soup = BeautifulSoup(html, 'lxml')
# 查找所有name为ul的标签
print(soup.find_all('ul'))
# 输出第一个ul标签的类型
print(type(soup.find_all('ul')[0]))
# 从ul中循环遍历取出所有的li标签
for ul in soup.find_all('ul'):
print(ul.find_all('li'))
attrs属性
from bs4 import BeautifulSoup
html = '''
Hello
- Foo
- Bar
- Jay
- Foo
- Bar
'''
soup = BeautifulSoup(html, 'lxml')
# attrs传递的是字典形式
print(soup.find_all(attrs={'id': 'list-1'}))
print(soup.find_all(attrs={'name': 'elements'}))
print(soup.find_all(id="list-1"))
# 因为class是Python中的一个关键字，所以不能直接用它来传数据
print(soup.find_all(class_="element"))
text属性
做元素查找不方便。
from bs4 import BeautifulSoup
html = '''
Hello
- Foo
- Bar
- Jay
- Foo
- Bar
'''
soup = BeautifulSoup(html, 'lxml')
# 根据文本内容选择
print(soup.find_all(text='Foo'))
2、find(name, attrs, recursive, text, **kwargs)
find返回单个元素，即匹配到的第一个结果。
from bs4 import BeautifulSoup
html = '''
Hello
- Foo
- Bar
- Jay
- Foo
- Bar
'''
soup = BeautifulSoup(html, 'lxml')
print(soup.find('ul'))
print(type(soup.find('ul')))
print(soup.find('page'))
其他一些类似的方法
（1）、find_parents() VS find_patent()
find_parents() ——返回所有祖先节点
find_patent() ——返回直接父节点
（2）、find_next_siblings() VS find_next_sibling
find_next_siblings() ——返回后面所有兄弟节点
find_next_sibling() ——返回后面第一个兄弟节点
（3）、find_previous_siblings() VS find_previous_sibling()
find_previous_siblings() ——返回前面所有兄弟节点
find_previous_sibling() ——返回前面第一个兄弟节点
（4）、find_all_next() VS find_next()
find_all_next() ——返回节点后所有符合条件的节点
find_next() ——返回第一个符合条件的节点
（5）、find_all_previous() VS find_previous()
find_all_previous() —— 返回节点前所有符合条件的节点
find_previous() —— 返回节点前第一个符合条件的节点
2.4 CSS选择器
通过select()直接传入CSS选择器即可完成选择。
from bs4 import BeautifulSoup
html = '''
Hello
- Foo
- Bar
- Jay
- Foo
- Bar
'''
soup = BeautifulSoup(html, 'lxml')
# 选择class属性，用空格分隔
print(soup.select('.panel .panel-heading'))
# 选择ul标签中的li标签
print(soup.select('ul li'))
# 选择 ID 中的class为element的标签
print(soup.select('#list-2 .element'))
# 输出第一个ul标签的类型
print(type(soup.select('ul')[0]))
（1）获取属性
html='''
Hello
- Foo
- Bar
- Jay
- Foo
- Bar
'''
from bs4 import BeautifulSoup
soup = BeautifulSoup(html, 'lxml')
for ul in soup.select('ul'):
print(ul['id'])
print(ul.attrs['id'])
（2）获取内容
from bs4 import BeautifulSoup
html = '''
Hello
- Foo
- Bar
- Jay
- Foo
- Bar
'''
soup = BeautifulSoup(html, 'lxml')
for li in soup.select('li'):
# get_text获取内容
print(li.get_text())
总结
1、推荐使用lxml解析库，必要时使用html.parser
2、标签选择筛选功能弱但是速度快
3、建议使用find()、find_all()查询匹配单个结果或者多个结果
4、如果对CSS选择器熟悉的建议使用select()方法
5、记住常用的获取属性和文本值得方法