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

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 = """
<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,
",
"
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))
",
"
<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
"
<a class="sister" href="http://example.com/tillie" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" id="link3">Tillie</a>
";
and they lived at the bottom of a well."
for sibling in soup.find(id="link3").previous_siblings:
  print(repr(sibling))
" and
"
<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/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
"

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
"

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"
";
and they lived at the bottom of a well."
"
"
<p class="story">...</p>
"..."
"
"

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