第四章 MySQL鎖機制
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下面就是使用Python爬蟲庫BeautifulSoup對文件樹進行遍歷並對標籤進行操作的例項,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迴圈
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的子孫節點進行遞迴迴圈
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型別的子節點,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包含多個字串,可以使用.strings迴圈獲取
for string in soup.strings: print(string)
The Dormouse's storyThe Dormouse's story
Once upon a time there were three little sisters; and their names were
Elsie
,Lacie
andTillie
;
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>
字串也有父節點
title_tag.string.parent
<title>The Dormouse's story</title>
2.parents:遞迴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>
在實際文件中.next_sibling和previous_sibling通常是字串或者空白符
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物件(字串或tag),即深度優先遍歷的後序節點和前序節點
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可以向前或向後訪問文件的解析內容,就好像文件正在被解析一樣
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'
更多關於使用Python爬蟲庫BeautifulSoup遍歷文件樹並對標籤進行操作的方法與文章大家可以點選下面的相關文章