爬虫之BeautifulSoup库
文档：https://beautifulsoup.readthedocs.io/zh_CN/latest/
一、开始
解析库
# 安装解析库
pip3 install lxml
pip3 install html5lib
基本使用
html = """
<html>
<head>
<title>The Dormouse's story</title>
</head>
<body>
<p class="title" name="dromouse"><b>The Dormouse's story</b></p>
"""
from bs4 import BeautifulSoup
soup = BeautifulSoup(html, "lxml")
print(soup.prettify()) # 格式化代码，自动补全，容错处理
print(soup.title.string) # The Dormouse's story
"""
<html>
<head>
<title>The Dormouse's story</title>
</head>
<body>
<p class="title" name="dromouse"><b>The Dormouse's story</b></p>
</body>
</html>
"""
二、标签选择器
选择元素
html = """
<html>
<head>
<title>The Dormouse's story</title>
</head>
<body>
<p class="title" name="dromouse"><b>The Dormouse's story</b></p>
<p class="story">
beautifulsoup4
<a class="sister" href="http://example.com/elsie" id="link1">Elsie</a>
<a class="sister" href="http://example.com/lacie" id="link2">Lacie</a>
<a class="sister" href="http://example.com/tillie" id="link3">Tillie</a>
</p>
<p class="story">...</p>
</body>
</html>
"""
from bs4 import BeautifulSoup
soup = BeautifulSoup(html, "lxml")
print(soup.title) # <title>The Dormouse's story</title>
print(type(soup.title)) # <class 'bs4.element.Tag'>
print(soup.head)
"""
<head>
<title>The Dormouse's story</title>
</head>
"""
print(soup.p) # <p class="title" name="dromouse"><b>The Dormouse's story</b></p>
获取名称
from bs4 import BeautifulSoup
html = "<html><title>The Dormouse's story</title></html>"
soup = BeautifulSoup(html, "lxml")
print(soup.title.name) # title
获取属性值
from bs4 import BeautifulSoup
html = """
<p class="title" name="pd"><b>The Dormouse's story</b></p>
"""
soup = BeautifulSoup(html, "lxml")
print(soup.p.attrs["name"]) # pd
print(soup.p["name"]) # pd
获取内容
from bs4 import BeautifulSoup
html = """
<p class="title" name="pd"><b>The Dormouse's story</b></p>
"""
soup = BeautifulSoup(html, "lxml")
print(soup.p.string) # The Dormouse's story
嵌套选择
from bs4 import BeautifulSoup
html = """
<head>
<title>The Dormouse's story</title>
</head>
"""
soup = BeautifulSoup(html, "lxml")
print(soup.head.title.string) # The Dormouse's story
子节点和子孙节点
tag的 .contents 属性可以将tag的子节点以列表的方式输出：
from bs4 import BeautifulSoup
html = """
<p class="story">
beautifulsoup4
<a class="sister" href="http://example.com/elsie" id="link1">Elsie</a>
<a class="sister" href="http://example.com/lacie" id="link2">Lacie</a>
<a class="sister" href="http://example.com/tillie" id="link3">Tillie</a>
</p>
"""
soup = BeautifulSoup(html, "lxml")
print(soup.p.contents)
# ['\nbeautifulsoup4\n', <a class="sister" href="http://example.com/elsie" id="link1">Elsie</a>, '\n', <a class="sister" href="http://example.com/lacie" id="link2">Lacie</a>, '\n', <a class="sister" href="http://example.com/tillie" id="link3">Tillie</a>, '\n']
通过tag的 .children 生成器，可以对tag的子节点进行循环：
html = """
<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>
"""
from bs4 import BeautifulSoup
soup = BeautifulSoup(html, "lxml")
print(soup.p.children) # <list_iterator object at 0x00000000031F6C88>
for i, child in enumerate(soup.p.children):
print(i, child) # 0 <b>The Dormouse's story</b>
.contents 和 .children 属性仅包含tag的直接子节点。例如，<head>标签只有一个直接子节点<title>；
但是<title>标签也包含一个子节点：字符串 "The Dormouse’s story"，这种情况下字符串 "The Dormouse’s story" 也属于<head>标签的子孙节点，.descendants 属性可以对所有tag的子孙节点进行递归循环：
html = """
<html>
<head><title>The Dormouse's story</title></head>
<body>
<p class="title"><b>The Dormouse's story</b></p>
<p class="story">...</p>
"""
from bs4 import BeautifulSoup
soup = BeautifulSoup(html, "lxml")
print(soup.p.descendants) # <generator object descendants at 0x0000000000727200>
for i, child in enumerate(soup.p.descendants):
print(i, child)
"""
0 <b>The Dormouse's story</b>
1 The Dormouse's story
"""
上面的例子中,，<head>标签只有一个子节点，但是有2个子孙节点。
父节点和祖先节点
通过 .parent 属性来获取某个元素的父节点：
html = """
<p class="title"><b>The Dormouse's story</b></p>
"""
from bs4 import BeautifulSoup
soup = BeautifulSoup(html, "lxml")
print(soup.b.parent) # <p class="title"><b>The Dormouse's story</b></p>
通过元素的 .parents 属性可以递归得到元素的所有父辈节点：
html = """
<html><head><title>The Dormouse's story</title></head></html>
"""
from bs4 import BeautifulSoup
soup = BeautifulSoup(html, "lxml")
print(soup.title.parents) # <generator object parents at 0x0000000000AA7200>
for i, parent in enumerate(soup.title.parents):
print(i, parent)
"""
0 <head><title>The Dormouse's story</title></head>
1 <html><head><title>The Dormouse's story</title></head></html>
2 <html><head><title>The Dormouse's story</title></head></html>
"""
兄弟节点
html = """
<p class="story">
Once upon a time there were three little sisters
<a id="link1">Elsie</a>
<a id="link2">Lacie</a>
<a id="link3">Tillie</a>
they lived at the bottom of a well
</p> """
from bs4 import BeautifulSoup
soup = BeautifulSoup(html, "lxml")
print(list(soup.a.next_siblings))
print(list(soup.a.previous_siblings))
"""
['\n', <a id="link2">Lacie</a>, '\n', <a id="link3">Tillie</a>, '\nthey lived at the bottom of a well\n']
['\nOnce upon a time there were three little sisters\n']
"""
三、标准选择器
find_all(name , attrs , recursive , text , **kwargs)
name参数
html = """
<div class="panel">
<div class="panel-heading">
<h4>Hello</h4>
</div>
<div class="panel-body">
<ul class="list" id="list-1">
<li class="element">Foo</li>
<li class="element">Bar</li>
<li class="element">Jay</li>
</ul>
<ul class="list list-small" id="list-2">
<li class="element">Foo</li>
<li class="element">Bar</li>
</ul>
</div>
</div>
"""
from bs4 import BeautifulSoup
soup = BeautifulSoup(html, "lxml")
print(soup.find_all("ul"))
"""
[<ul class="list" id="list-1">
<li class="element">Foo</li>
<li class="element">Bar</li>
<li class="element">Jay</li>
</ul>, <ul class="list list-small" id="list-2">
<li class="element">Foo</li>
<li class="element">Bar</li>
</ul>]
"""
for ul in soup.find_all("ul"):
print(ul.find_all("li"))
"""
[<li class="element">Foo</li>, <li class="element">Bar</li>, <li class="element">Jay</li>]
[<li class="element">Foo</li>, <li class="element">Bar</li>]
"""
print(type(soup.find_all("ul")[0])) # <class 'bs4.element.Tag'>
attrs参数
html = """
<div class="panel">
<div class="panel-heading">
<h4>Hello</h4>
</div>
<div class="panel-body">
<ul class="list" id="list-1">
<li class="element">Foo</li>
<li class="element">Bar</li>
<li class="element">Jay</li>
</ul>
<ul class="list list-small" id="list-2">
<li class="element">Foo</li>
<li class="element">Bar</li>
</ul>
</div>
</div>
"""
from bs4 import BeautifulSoup
soup = BeautifulSoup(html, "lxml")
print(soup.find_all(attrs={"id": "list-1"}))
"""
[<ul class="list" id="list-1" name="elements">
<li class="element">Foo</li>
<li class="element">Bar</li>
<li class="element">Jay</li>
</ul>]
"""
或者不使用attrs
html = """
<div class="panel">
<div class="panel-heading">
<h4>Hello</h4>
</div>
<div class="panel-body">
<ul class="list" id="list-1">
<li class="element">Foo</li>
<li class="element">Bar</li>
<li class="element">Jay</li>
</ul>
</div>
</div>
"""
from bs4 import BeautifulSoup
soup = BeautifulSoup(html, "lxml")
print(soup.find_all(id="list-1"))
"""
[<ul class="list" id="list-1">
<li class="element">Foo</li>
<li class="element">Bar</li>
<li class="element">Jay</li>
</ul>]
"""
print(soup.find_all(class_="element"))
# [<li class="element">Foo</li>, <li class="element">Bar</li>, <li class="element">Jay</li>]
text参数：不是返回标签，而是返回内容
html = """
<div class="panel">
<div class="panel-heading">
<h4>Hello</h4>
</div>
<div class="panel-body">
<ul class="list" id="list-1">
<li class="element">Foo</li>
<li class="element">Bar</li>
<li class="element">Jay</li>
</ul>
<ul class="list list-small" id="list-2">
<li class="element">Foo</li>
<li class="element">Bar</li>
</ul>
</div>
</div>
"""
from bs4 import BeautifulSoup
soup = BeautifulSoup(html, "lxml")
print(soup.find_all(text="Foo")) # ['Foo', 'Foo']
find( name , attrs , recursive , text , **kwargs )
find返回单个元素，find_all返回所有元素。
html = """
<div class="panel">
<div class="panel-heading">
<h4>Hello</h4>
</div>
<div class="panel-body">
<ul class="list" id="list-1">
<li class="element">Foo</li>
<li class="element">Bar</li>
<li class="element">Jay</li>
</ul>
<ul class="list list-small" id="list-2">
<li class="element">Foo</li>
<li class="element">Bar</li>
</ul>
</div>
</div>
"""
from bs4 import BeautifulSoup
soup = BeautifulSoup(html, "lxml")
print(soup.find("ul"))
"""
<ul class="list" id="list-1">
<li class="element">Foo</li>
<li class="element">Bar</li>
<li class="element">Jay</li>
</ul>
"""
print(soup.find("page")) # None
find_parents() 和 find_parent()
find_parents()返回所有祖先节点，find_parent()返回直接父节点。
find_next_siblings() 和 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。
find_previous_siblings() 和 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。
find_all_next() 和 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。
find_all_previous() 和 find_previous()
find_all_previous()返回节点后所有符合条件的节点，find_previous()返回第一个符合条件的节点。
四、CSS选择器
通过select()直接传入CSS选择器即可完成选择。
html = """
<div class="panel">
<div class="panel-heading">
<h4>Hello</h4>
</div>
<div class="panel-body">
<ul class="list" id="list-1">
<li class="element">Foo</li>
<li class="element">Bar</li>
<li class="element">Jay</li>
</ul>
<ul class="list list-small" id="list-2">
<li class="element">Foo</li>
<li class="element">Bar</li>
</ul>
</div>
</div>
"""
from bs4 import BeautifulSoup
soup = BeautifulSoup(html, "lxml")
print(soup.select(".panel .panel-heading"))
"""
[<div class="panel-heading">
<h4>Hello</h4>
</div>]
"""
print(soup.select("ul li"))
# [<li class="element">Foo</li>, <li class="element">Bar</li>, <li class="element">Jay</li>, <li class="element">Foo</li>, <li class="element">Bar</li>]
print(soup.select("#list-2 .element"))
# [<li class="element">Foo</li>, <li class="element">Bar</li>]
print(soup.select("ul")[1])
"""
<ul class="list list-small" id="list-2">
<li class="element">Foo</li>
<li class="element">Bar</li>
</ul>
"""
html = """
<div class="panel">
<div class="panel-heading">
<h4>Hello</h4>
</div>
<div class="panel-body">
<ul class="list" id="list-1">
<li class="element">Foo</li>
<li class="element">Bar</li>
<li class="element">Jay</li>
</ul>
<ul class="list list-small" id="list-2">
<li class="element">Foo</li>
<li class="element">Bar</li>
</ul>
</div>
</div>
"""
from bs4 import BeautifulSoup
soup = BeautifulSoup(html, "lxml")
for ul in soup.select("ul"):
print(ul.select("li"))
"""
[<li class="element">Foo</li>, <li class="element">Bar</li>, <li class="element">Jay</li>]
[<li class="element">Foo</li>, <li class="element">Bar</li>]
"""
获取属性：
html = """
<div class="panel">
<div class="panel-heading">
<h4>Hello</h4>
</div>
<div class="panel-body">
<ul class="list" id="list-1">
<li class="element">Foo</li>
<li class="element">Bar</li>
<li class="element">Jay</li>
</ul>
<ul class="list list-small" id="list-2">
<li class="element">Foo</li>
<li class="element">Bar</li>
</ul>
</div>
</div>
"""
from bs4 import BeautifulSoup
soup = BeautifulSoup(html, "lxml")
for ul in soup.select("ul"):
print(ul["id"])
print(ul.attrs["id"])
"""
list-1
list-1
list-2
list-2
"""
获取内容：
html = """
<div class="panel">
<div class="panel-heading">
<h4>Hello</h4>
</div>
<div class="panel-body">
<ul class="list" id="list-1">
<li class="element">Foo</li>
<li class="element">Bar</li>
<li class="element">Jay</li>
</ul>
<ul class="list list-small" id="list-2">
<li class="element">Foo</li>
<li class="element">Bar</li>
</ul>
</div>
</div>
"""
from bs4 import BeautifulSoup
soup = BeautifulSoup(html, "lxml")
for li in soup.select("li"):
print(li.get_text())
"""
Foo
Bar
Jay
Foo
Bar
"""
五、总结
- 推荐使用lxml解析库，必要时使用html.parser
- 标签选择筛选功能弱但是速度快
- 建议使用find()、find_all() 查询匹配单个结果或者多个结果
- 如果对CSS选择器熟悉建议使用select()
- 记住常用的获取属性和文本值的方法
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