编程 Python

使用Python爬虫库BeautifulSoup遍历文档树并对标签进行操作详解

Posted in Python onJanuary 25, 2020

下面就是使用Python爬虫库BeautifulSoup对文档树进行遍历并对标签进行操作的实例，都是最基础的内容

html_doc = """
<html><head><title>The Dormouse's story</title></head>

<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" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" class="sister" id="link1">Elsie</a>,
<a href="http://example.com/lacie" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" class="sister" id="link2">Lacie</a> and
<a href="http://example.com/tillie" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" 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_doc,'lxml')

一、子节点

一个Tag可能包含多个字符串或者其他Tag，这些都是这个Tag的子节点.BeautifulSoup提供了许多操作和遍历子结点的属性。

1.通过Tag的名字来获得Tag

print(soup.head)
print(soup.title)

<head><title>The Dormouse's story</title></head>
<title>The Dormouse's story</title>

通过名字的方法只能获得第一个Tag，如果要获得所有的某种Tag可以使用find_all方法

soup.find_all('a')

[<a class="sister" href="http://example.com/elsie" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" id="link1">Elsie</a>,
 <a class="sister" href="http://example.com/lacie" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" id="link2">Lacie</a>,
 <a class="sister" href="http://example.com/tillie" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" id="link3">Tillie</a>]

2.contents属性：将Tag的子节点通过列表的方式返回

head_tag = soup.head
head_tag.contents

[<title>The Dormouse's story</title>]

title_tag = head_tag.contents[0]
title_tag

<title>The Dormouse's story</title>

title_tag.contents

["The Dormouse's story"]

3.children：通过该属性对子节点进行循环

for child in title_tag.children:
  print(child)

The Dormouse's story

4.descendants：不论是contents还是children都是返回直接子节点，而descendants对所有tag的子孙节点进行递归循环

for child in head_tag.children:
  print(child)

<title>The Dormouse's story</title>

for child in head_tag.descendants:
  print(child)

<title>The Dormouse's story</title>
The Dormouse's story

5.string 如果tag只有一个NavigableString类型的子节点，那么tag可以使用.string得到该子节点

title_tag.string

"The Dormouse's story"

如果一个tag只有一个子节点，那么使用.string可以获得其唯一子结点的NavigableString.

head_tag.string

"The Dormouse's story"

如果tag有多个子节点，tag无法确定.string对应的是那个子结点的内容，故返回None

print(soup.html.string)

None

6.strings和stripped_strings

如果tag包含多个字符串，可以使用.strings循环获取

for string in soup.strings:
  print(string)

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.


...

.string输出的内容包含了许多空格和空行，使用strpped_strings去除这些空白内容

for string in soup.stripped_strings:
  print(string)

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.
...

二、父节点

1.parent：获得某个元素的父节点

title_tag = soup.title
title_tag.parent

<head><title>The Dormouse's story</title></head>

字符串也有父节点

title_tag.string.parent

<title>The Dormouse's story</title>

2.parents：递归的获得所有父辈节点

link = soup.a
for parent in link.parents:
  if parent is None:
    print(parent)
  else:
    print(parent.name)

p
body
html
[document]

三、兄弟结点

sibling_soup = BeautifulSoup("<a><b>text1</b><c>text2</c></b></a>",'lxml')
print(sibling_soup.prettify())

<html>
 <body>
 <a>
  <b>
  text1
  </b>
  <c>
  text2
  </c>
 </a>
 </body>
</html>

1.next_sibling和previous_sibling

sibling_soup.b.next_sibling

<c>text2</c>

sibling_soup.c.previous_sibling

<b>text1</b>

在实际文档中.next_sibling和previous_sibling通常是字符串或者空白符

soup.find_all('a')

[<a class="sister" href="http://example.com/elsie" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" id="link1">Elsie</a>,
 <a class="sister" href="http://example.com/lacie" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" id="link2">Lacie</a>,
 <a class="sister" href="http://example.com/tillie" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" id="link3">Tillie</a>]

soup.a.next_sibling # 第一个<a></a>的next_sibling是,\n

',\n'

soup.a.next_sibling.next_sibling

<a class="sister" href="http://example.com/lacie" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" id="link2">Lacie</a>

2.next_siblings和previous_siblings

for sibling in soup.a.next_siblings:
  print(repr(sibling))

',\n'
<a class="sister" href="http://example.com/lacie" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" id="link2">Lacie</a>
' and\n'
<a class="sister" href="http://example.com/tillie" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" id="link3">Tillie</a>
';\nand they lived at the bottom of a well.'

for sibling in soup.find(id="link3").previous_siblings:
  print(repr(sibling))

' and\n'
<a class="sister" href="http://example.com/lacie" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" id="link2">Lacie</a>
',\n'
<a class="sister" href="http://example.com/elsie" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" id="link1">Elsie</a>
'Once upon a time there were three little sisters; and their names were\n'

四、回退与前进

1.next_element和previous_element

指向下一个或者前一个被解析的对象(字符串或tag)，即深度优先遍历的后序节点和前序节点

last_a_tag = soup.find("a", id="link3")
print(last_a_tag.next_sibling)
print(last_a_tag.next_element)

;
and they lived at the bottom of a well.
Tillie

last_a_tag.previous_element

' and\n'

2.next_elements和previous_elements

通过.next_elements和previous_elements可以向前或向后访问文档的解析内容，就好像文档正在被解析一样

for element in last_a_tag.next_elements:
  print(repr(element))

'Tillie'
';\nand they lived at the bottom of a well.'
'\n'
<p class="story">...</p>
'...'
'\n'

更多关于使用Python爬虫库BeautifulSoup遍历文档树并对标签进行操作的方法与文章大家可以点击下面的相关文章

使用Python爬虫库BeautifulSoup遍历文档树并对标签进行操作详解

- Author -

BQW_

声明：登载此文出于传递更多信息之目的，并不意味着赞同其观点或证实其描述。

Python 相关文章推荐

python实现逆波兰计算表达式实例详解

May 06 Python

介绍Python中的fabs()方法的使用

May 14 Python

Python的socket模块源码中的一些实现要点分析

Jun 06 Python

Python的Flask框架应用调用Redis队列数据的方法

Jun 06 Python

Python中struct模块对字节流/二进制流的操作教程

Jan 21 Python

python清除字符串中间空格的实例讲解

May 11 Python

python中pip的安装与使用教程

Aug 10 Python

python+flask实现API的方法

Nov 21 Python

python3实现逐字输出的方法

Jan 23 Python

python实现抠图给证件照换背景源码

Aug 20 Python

requests在python中发送请求的实例讲解

Feb 17 Python

Python机器学习之逻辑回归

May 11 Python

Python爬虫库BeautifulSoup获取对象(标签)名,属性,内容,注释

Jan 25 #Python

Python爬虫库BeautifulSoup的介绍与简单使用实例

Jan 25 #Python

使用Python爬虫库requests发送表单数据和JSON数据

Jan 25 #Python

Python爬虫库requests获取响应内容、响应状态码、响应头

Jan 25 #Python

使用Python爬虫库requests发送请求、传递URL参数、定制headers

Jan 25 #Python

flask框架自定义url转换器操作详解

Jan 25 #Python

常用python爬虫库介绍与简要说明

Jan 25 #Python