使用Python爬蟲庫BeautifulSoup遍歷文檔樹并對標簽進行操作詳解

更新時間：2020年01月25日 16:19:08 作者：BQW_

今天為大家介紹下Python爬蟲庫BeautifulSoup遍歷文檔樹并對標簽進行操作的詳細方法與函數(shù)

下面就是使用Python爬蟲庫BeautifulSoup對文檔樹進行遍歷并對標簽進行操作的實例，都是最基礎(chǔ)的內(nèi)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  rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" class="sister" id="link1">Elsie</a>,
<a  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  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、子節(jié)點

一個Tag可能包含多個字符串或者其他Tag，這些都是這個Tag的子節(jié)點.BeautifulSoup提供了許多操作和遍歷子結(jié)點的屬性。

1.通過Tag的名字來獲得Tag

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

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

通過名字的方法只能獲得第一個Tag，如果要獲得所有的某種Tag可以使用find_all方法

soup.find_all('a')

[<a class="sister"  rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" id="link1">Elsie</a>,
 <a class="sister"  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"  rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" id="link3">Tillie</a>]

2.contents屬性：將Tag的子節(jié)點通過列表的方式返回

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：通過該屬性對子節(jié)點進行循環(huán)

for child in title_tag.children:
  print(child)

The Dormouse's story

4.descendants：不論是contents還是children都是返回直接子節(jié)點，而descendants對所有tag的子孫節(jié)點進行遞歸循環(huán)

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只有一個NavigableString類型的子節(jié)點，那么tag可以使用.string得到該子節(jié)點

title_tag.string

"The Dormouse's story"

如果一個tag只有一個子節(jié)點，那么使用.string可以獲得其唯一子結(jié)點的NavigableString.

head_tag.string

"The Dormouse's story"

如果tag有多個子節(jié)點，tag無法確定.string對應(yīng)的是那個子結(jié)點的內(nèi)容，故返回None

print(soup.html.string)

None

6.strings和stripped_strings

如果tag包含多個字符串，可以使用.strings循環(huán)獲取

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輸出的內(nèi)容包含了許多空格和空行，使用strpped_strings去除這些空白內(nèi)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、父節(jié)點

1.parent：獲得某個元素的父節(jié)點

title_tag = soup.title
title_tag.parent

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

字符串也有父節(jié)點

title_tag.string.parent

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

2.parents：遞歸的獲得所有父輩節(jié)點

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

p
body
html
[document]

三、兄弟結(jié)點

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>

在實際文檔中.next_sibling和previous_sibling通常是字符串或者空白符

soup.find_all('a')

[<a class="sister"  rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" id="link1">Elsie</a>,
 <a class="sister"  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"  rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" id="link3">Tillie</a>]

soup.a.next_sibling # 第一個<a></a>的next_sibling是,\n

',\n'

soup.a.next_sibling.next_sibling

<a class="sister"  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"  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"  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"  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"  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、回退與前進

1.next_element和previous_element

指向下一個或者前一個被解析的對象(字符串或tag)，即深度優(yōu)先遍歷的后序節(jié)點和前序節(jié)點

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

通過.next_elements和previous_elements可以向前或向后訪問文檔的解析內(nèi)容，就好像文檔正在被解析一樣

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'

更多關(guān)于使用Python爬蟲庫BeautifulSoup遍歷文檔樹并對標簽進行操作的方法與文章大家可以點擊下面的相關(guān)文章

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