今天爲大家介紹下Python爬蟲庫BeautifulSoup遍歷文檔樹並對標籤進行操作的詳細方法與函數
下面就是使用Python爬蟲庫BeautifulSoup對文檔樹進行遍歷並對標籤進行操作的實例，都是最基礎的內容
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、子節點
一個Tag可能包含多個字符串或者其他Tag，這些都是這個Tag的子節點.BeautifulSoup提供了許多操作和遍歷子結點的屬性。
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" 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屬性：將Tag的子節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：通過該屬性對子節點進行循環
for child in title_tag.children:
print(child)
The Dormouse's story
4.descendants： 不論是contents還是children都是返回直接子節點，而descendants對所有tag的子孫節點進行遞歸循環
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類型的子節點，那麼tag可以使用.string得到該子節點
title_tag.string
"The Dormouse's story"
如果一個tag只有一個子節點，那麼使用.string可以獲得其唯一子結點的NavigableString.
head_tag.string
"The Dormouse's story"
如果tag有多個子節點，tag無法確定.string對應的是那個子結點的內容，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輸出的內容包含了許多空格和空行，使用strpped_strings去除這些空白內容
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、父節點
1.parent：獲得某個元素的父節點
title_tag = soup.title
title_tag.parent
<head><title>The Dormouse's story</title></head>
字符串也有父節點
title_tag.string.parent
<title>The Dormouse's story</title>
2.parents：遞歸的獲得所有父輩節點
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" 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>]
oup.a.next_sibling # 第一個<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)，即深度優先遍歷的後序節點和前last_a_tag =
soup.find("a", id="link3")
print(last_a_tag.next_sibling)
print(last_a_tag.next_element)
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可以向前或向後訪問文檔的解析內容，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'
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