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>
"""

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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>

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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)
# ['
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>, '
']

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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>

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.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
"""

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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>
"""

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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))
"""
['
', <a id="link2">Lacie</a>, '
', <a id="link3">Tillie</a>, '
they lived at the bottom of a well
']
['
Once upon a time there were three little sisters
']
"""

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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'>

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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>]
"""

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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>]

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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']

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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

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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>
"""

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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>]
"""

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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
"""

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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
"""

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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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原文地址：https://www.cnblogs.com/believepd/p/10657866.html