Python写爬虫你要了解的Bs4模块

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发布于 2020-07-22 16:47:02

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发布于 2020-07-22 16:47:02

什么是BS4？

BS4全称是Beatiful Soup，官方文档[1]它提供一些简单的、python式的函数用来处理导航、搜索、修改分析树等功能。它是一个工具箱，通过解析文档为tiful Soup自动将输入文档转换为Unicode编码，输出文档转换为utf-8编码。python写爬虫使用较多的一个模块。参考文章[2]

快速上手

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">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.prettify())
print(soup.title.string)

标签选择器

属性	功能	使用eg
title	选择元素	soup.title
head	选择元素	soup.head
p	选择元素	soup.p
name	获取名称	soup.title.name
attrs	获取属性	soup.p.attrs['name']或soup.p['name']
string	获取内容	soup.p.string或者soup.p.text
contents	获取子节点，返回list	soup.p.contents
children	获取子节点，返回迭代器	soup.p.children
descendants	获取子孙节点，返回迭代器	soup.p.descendants
parent	获取父节点,返回列表	soup.a.parent
parents	获取祖先节点,返回列表	soup.a.parents
next_siblings	获取后面的兄弟节点,返回列表	soup.a.next_siblings
previous_siblings	获取前面的兄弟节点,返回列表	soup.a.previous_siblings

标准选择器

find_all(name,attrs,recursive,text,**kwargs)

可根据标签名、属性、内容查找文档

html='''
<div class="panel">
    <div class="panel-heading">
        <h4>Hello</h4>
    </div>
    <div class="panel-body">
        <ul class="list" id="list-1" name="elements">
            <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'}))
print(soup.find_all(attrs={'name': 'elements'}))
# 用法不同，结果相同
print(soup.find_all(id='list-1'))
print(soup.find_all(class_='element'))
print(soup.find_all(text='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'))
print(type(soup.find('ul')))
print(soup.find('page'))

>>>>>

<ul class="list" id="list-1">
<li class="element">Foo</li>
<li class="element">Bar</li>
<li class="element">Jay</li>
</ul>
<class 'bs4.element.Tag'>
None

方法	描述
prettify	格式化html代码
find_parents()	返回所有祖先节点
find_parent()	返回直接父节点
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()	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()	返回节点
find_next()	返回第一个符合条件的节点
find_all_previous()	返回节点
find_previous()	返回第一个符合条件的节点

css选择器

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'))
print(soup.select('ul li'))
print(soup.select('#list-2 .element'))
print(type(soup.select('ul')[0]))
for li in soup.select('li'):
    print(li.get_text())