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

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 = """


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.

...
"""

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)

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')

[Elsie,
 Lacie,
 Tillie]

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_tag = head_tag.contents[0]
title_tag

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)

for child in head_tag.descendants:
  print(child)

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

字符串也有父节点

title_tag.string.parent

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("text1text2",'lxml')
print(sibling_soup.prettify())

 
 
  
  text1
  
  
  text2
  
 
 

1.next_sibling和previous_sibling

sibling_soup.b.next_sibling

text2

sibling_soup.c.previous_sibling

text1

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')

[Elsie,
 Lacie,
 Tillie]

soup.a.next_sibling # 第一个的next_sibling是,n

',n'

soup.a.next_sibling.next_sibling

Lacie

2.next_siblings和previous_siblings

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

',n'
Lacie
' andn'
Tillie
';nand they lived at the bottom of a well.'

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

' andn'
Lacie
',n'
Elsie
'once upon a time there were three little sisters; and their names weren'

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

' andn'

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'
...
'...'
'n'

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