python BeautifulSoup库详解

BeautifulSoup

Beautiful Soup 是一个可以从HTML或XML文件中提取数据的Python库.它能够通过你喜欢的转换器实现惯用的文档导航,查找,修改文档的方式

官方文档链接，相同效果的库还有pyquery模块，详见此

解析器

对网页进行析取时，若未规定解析器，此时使用的是python内部默认的解析器“html.parser”。

解析器是什么呢？ BeautifulSoup做的工作就是对html标签进行解释和分类，不同的解析器对相同html标签会做出不同解释。

举个官方文档上的例子：

BeautifulSoup("<a></p>", "lxml")
# <html><body><a></a></body></html>
BeautifulSoup("<a></p>", "html5lib")
# <html><head></head><body><a><p></p></a></body></html>
BeautifulSoup("<a></p>", "html.parser")
# <a></a>

官方文档上多次提到推荐使用"lxml"和"html5lib"解析器，因为默认的"html.parser"自动补全标签的功能很差，经常会出问题。

Parser	Typical usage	Advantages	Disadvantages
Python’s html.parser	`BeautifulSoup(markup,"html.parser")`	Batteries included Decent speed Lenient (as of Python 2.7.3 and 3.2.)	Not very lenient (before Python 2.7.3 or 3.2.2)
lxml’s HTML parser	`BeautifulSoup(markup,"lxml")`	Very fast Lenient	External C dependency
lxml’s XML parser	`BeautifulSoup(markup,"lxml-xml")` `BeautifulSoup(markup,"xml")`	Very fast The only currently supported XML parser	External C dependency
html5lib	`BeautifulSoup(markup,"html5lib")`	Extremely lenient Parses pages the same way a web browser does Creates valid HTML5	Very slow External Python dependency

可以看出，“lxml”的解析速度非常快，对错误也有一定的容忍性。“html5lib”对错误的容忍度是最高的，而且一定能解析出合法的html5代码，但速度很慢。

我们在实际爬取网站的时候，原网页的编码方式不统一，其中有一句乱码，用“html.parser”和“lxml”都解析到乱码的那句，后面的所有标签都被忽略了。而“html5lib”能够完美解决这个问题。

安装及基本使用

安装：

#安装 Beautiful Soup
pip install beautifulsoup4

#安装解析器
Beautiful Soup支持Python标准库中的HTML解析器,还支持一些第三方的解析器,其中一个是 lxml .根据操作系统不同,可以选择下列方法来安装lxml:

$ apt-get install Python-lxml

$ easy_install lxml

$ pip install lxml

另一个可供选择的解析器是纯Python实现的 html5lib , html5lib的解析方式与浏览器相同,可以选择下列方法来安装html5lib:

$ apt-get install Python-html5lib

$ easy_install html5lib

$ pip install html5lib

简单使用：

html_doc = """
<html><head><title>The Dormouse's story</title></head>
<body>
<p class="title"><b>The Dormouse's story</b></p>

<p class="story">Once upon a time there were three little sisters; and their names were
<a href="http://example.com/elsie" class="sister" id="link1">Elsie</a>,
<a href="http://example.com/lacie" class="sister" id="link2">Lacie</a> and
<a href="http://example.com/tillie" class="sister" id="link3">Tillie</a>;
and they lived at the bottom of a well.</p>

<p class="story">...</p>
"""

#基本使用：容错处理,文档的容错能力指的是在html代码不完整的情况下,使用该模块可以识别该错误。使用BeautifulSoup解析上述代码,能够得到一个 BeautifulSoup 的对象,并能按照标准的缩进格式的结构输出
from bs4 import BeautifulSoup
soup=BeautifulSoup(html_doc,'lxml') #具有容错功能
res=soup.prettify() #处理好缩进，结构化显示
print(res)

各种api详解

1. name，标签名称

import requests
from bs4 import BeautifulSoup

ret = requests.get(url="https://www.autohome.com.cn/news/")
soup = BeautifulSoup(ret.text, 'lxml')
print(type(soup))
# <class 'bs4.BeautifulSoup'>
tag = soup.find('a')
name = tag.name  # 获取
print("=" * 120)
print(tag)
# <a class="orangelink" href="//www.autohome.com.cn/beijing/cheshi/" target="_blank"><i class="topbar-icon topbar-icon16 topbar-icon16-building"></i>进入北京车市</a>
print(type(tag))
# <class 'bs4.element.Tag'>
print("=" * 120)

print(name)  # a
tag.name = 'span'  # 设置，将标签设置为span
print(soup)  # a标签已经被修改成了span标签
# <html>....<span class="orangelink" href="//www.autohome.com.cn/beijing/cheshi/" target="_blank"><i class="topbar-icon topbar-icon16 topbar-icon16-building"></i>进入北京车市</span>....</html>

　　soup类型为BeautifulSoup，tag类型为bs4.element.tag，下面是tag的一些属性

2. attr，标签属性

tag = soup.find('a')
attrs = tag.attrs  # 获取
print(tag)
# <a class="orangelink" href="//www.autohome.com.cn/beijing/cheshi/" target="_blank">
print(attrs)
# {'target': '_blank', 'href': '//www.autohome.com.cn/beijing/cheshi/', 'class': ['orangelink']}
tag.attrs = {'ik': 123}  # 设置
tag.attrs['id'] = 'iiiii'  # 添加
print(soup.find("a"))
# <a id="iiiii" ik="123">

2.5 contents 获取标签内所有内容

body = soup.find('body')
v = body.contents

3. children,所有子标签

# body = soup.find('body')
# v = body.children

4. descendants,所有子子孙孙标签

# body = soup.find('body')
# v = body.descendants

4.5 parent 父节点

body = soup.find('a')
v = body.parent

4.6 parents 获取所有祖先节点

body = soup.find('a')
v = body.parents
print(v)
# <generator object parents at 0x000001E1225C4E60>
是迭代器，要遍历输出

5. clear,将标签的所有子标签全部清空（保留标签名）

# tag = soup.find('body')
# tag.clear()
# print(soup)

6. decompose,递归的删除所有的标签

# body = soup.find('body')
# body.decompose()
# print(soup)

7. extract,递归的删除所有的标签，并获取删除的标签

# body = soup.find('body')
# v = body.extract()
# print(soup)

8. decode,转换为字符串（含当前标签）；decode_contents（不含当前标签）

# body = soup.find('body')
# v = body.decode()
# v = body.decode_contents()
# print(v)

9. encode,转换为字节（含当前标签）；encode_contents（不含当前标签）

# body = soup.find('body')
# v = body.encode()
# v = body.encode_contents()
# print(v)

10. find,获取匹配的第一个标签

# tag = soup.find('a')
# print(tag)
# tag = soup.find(name='a', attrs={'class': 'sister'}, recursive=True, text='Lacie')
# tag = soup.find(name='a', class_='sister', recursive=True, text='Lacie')
# print(tag)

11. find_all,获取匹配的所有标签

# tags = soup.find_all('a')
# print(tags)
 
# tags = soup.find_all('a',limit=1)
# print(tags)
 
# tags = soup.find_all(name='a', attrs={'class': 'sister'}, recursive=True, text='Lacie')
# # tags = soup.find(name='a', class_='sister', recursive=True, text='Lacie')
# print(tags)
 
 
# ####### 列表 #######
# v = soup.find_all(name=['a','div'])
# print(v)
 
# v = soup.find_all(class_=['sister0', 'sister'])
# print(v)
 
# v = soup.find_all(text=['Tillie'])
# print(v, type(v[0]))
 
 
# v = soup.find_all(id=['link1','link2'])
# print(v)
 
# v = soup.find_all(href=['link1','link2'])
# print(v)
 
# ####### 正则 #######
import re
# rep = re.compile('p')
# rep = re.compile('^p')
# v = soup.find_all(name=rep)
# print(v)
 
# rep = re.compile('sister.*')
# v = soup.find_all(class_=rep)
# print(v)
 
# rep = re.compile('http://www.oldboy.com/static/.*')
# v = soup.find_all(href=rep)
# print(v)
 
# ####### 方法筛选 #######
# def func(tag):
# return tag.has_attr('class') and tag.has_attr('id')
# v = soup.find_all(name=func)
# print(v)
 
 
# ## get,获取标签属性
# tag = soup.find('a')
# v = tag.get('id')
# print(v)

12. has_attr,检查标签是否具有该属性

# tag = soup.find('a')
# v = tag.has_attr('id')
# print(v)

13. get_text,获取标签内部文本内容

# tag = soup.find('a')
# v = tag.get_text('id')
# print(v)

14. index,检查标签在某标签中的索引位置

# tag = soup.find('body')
# v = tag.index(tag.find('div'))
# print(v)
 
# tag = soup.find('body')
# for i,v in enumerate(tag):
# print(i,v)

15. is_empty_element,是否是空标签(是否可以是空)或者自闭合标签，

判断是否是如下标签：'br' , 'hr', 'input', 'img', 'meta','spacer', 'link', 'frame', 'base'

# tag = soup.find('br')
# v = tag.is_empty_element
# print(v)

16. 兄弟节点，当前的关联标签

# soup.next
# soup.next_element
# soup.next_elements
# soup.next_sibling
# soup.next_siblings
 
#
# tag.previous
# tag.previous_element
# tag.previous_elements
# tag.previous_sibling
# tag.previous_siblings
 
#
# tag.parent
# tag.parents

17. 查找某标签的关联标签

# tag.find_next(...)
# tag.find_all_next(...)
# tag.find_next_sibling(...)
# tag.find_next_siblings(...)
 
# tag.find_previous(...)
# tag.find_all_previous(...)
# tag.find_previous_sibling(...)
# tag.find_previous_siblings(...)
 
# tag.find_parent(...)
# tag.find_parents(...)
 
# 参数同find_all

18. select,select_one, CSS选择器

soup.select("title")
 
soup.select("p nth-of-type(3)")
 
soup.select("body a")
 
soup.select("html head title")
 
tag = soup.select("span,a")
 
soup.select("head > title")
 
soup.select("p > a")
 
soup.select("p > a:nth-of-type(2)")
 
soup.select("p > #link1")
 
soup.select("body > a")
 
soup.select("#link1 ~ .sister")
 
soup.select("#link1 + .sister")
 
soup.select(".sister")
 
soup.select("[class~=sister]")
 
soup.select("#link1")
 
soup.select("a#link2")
 
soup.select('a[href]')
 
soup.select('a[href="http://example.com/elsie"]')
 
soup.select('a[href^="http://example.com/"]')
 
soup.select('a[href$="tillie"]')
 
soup.select('a[href*=".com/el"]')
 
 
from bs4.element import Tag
 
def default_candidate_generator(tag):
    for child in tag.descendants:
        if not isinstance(child, Tag):
            continue
        if not child.has_attr('href'):
            continue
        yield child
 
tags = soup.find('body').select("a", _candidate_generator=default_candidate_generator)
print(type(tags), tags)
 
from bs4.element import Tag
def default_candidate_generator(tag):
    for child in tag.descendants:
        if not isinstance(child, Tag):
            continue
        if not child.has_attr('href'):
            continue
        yield child
 
tags = soup.find('body').select("a", _candidate_generator=default_candidate_generator, limit=1)
print(type(tags), tags)

19. 标签的内容（str）

# tag = soup.find('span')
# print(tag.string)          # 获取
# tag.string = 'new content' # 设置
# print(soup)
 
# tag = soup.find('body')
# print(tag.string)
# tag.string = 'xxx'
# print(soup)
 
# tag = soup.find('body')
# v = tag.stripped_strings  # 递归内部获取所有标签的文本
# print(v)

20.append在当前标签内部追加一个标签

# tag = soup.find('body')
# tag.append(soup.find('a'))
# print(soup)
#
# from bs4.element import Tag
# obj = Tag(name='i',attrs={'id': 'it'})
# obj.string = '我是一个新来的'
# tag = soup.find('body')
# tag.append(obj)
# print(soup)

21.insert在当前标签内部指定位置插入一个标签

# from bs4.element import Tag
# obj = Tag(name='i', attrs={'id': 'it'})
# obj.string = '我是一个新来的'
# tag = soup.find('body')
# tag.insert(2, obj)
# print(soup)

22. insert_after,insert_before 在当前标签后面或前面插入

# from bs4.element import Tag
# obj = Tag(name='i', attrs={'id': 'it'})
# obj.string = '我是一个新来的'
# tag = soup.find('body')
# # tag.insert_before(obj)
# tag.insert_after(obj)
# print(soup)

23. replace_with 在当前标签替换为指定标签

# from bs4.element import Tag
# obj = Tag(name='i', attrs={'id': 'it'})
# obj.string = '我是一个新来的'
# tag = soup.find('div')
# tag.replace_with(obj)
# print(soup)

24. 创建标签之间的关系

# tag = soup.find('div')
# a = soup.find('a')
# tag.setup(previous_sibling=a)
# print(tag.previous_sibling)

25. wrap，将指定标签把当前标签包裹起来

# from bs4.element import Tag
# obj1 = Tag(name='div', attrs={'id': 'it'})
# obj1.string = '我是一个新来的'
#
# tag = soup.find('a')
# v = tag.wrap(obj1)
# print(soup)
 
# tag = soup.find('a')
# v = tag.wrap(soup.find('p'))
# print(soup)

26. unwrap，去掉当前标签，将保留其包裹的标签

# tag = soup.find('a')
# v = tag.unwrap()
# print(soup)

111