小编给大家分享一下Python爬虫中遍历文档树的方法，希望大家阅读完这篇文章后大所收获，下面让我们一起去探讨吧！
遍历文档树
1.直接子节点：.contents .children属性
.content
Tag的.content属性可以将Tag的子节点以列表的方式输出
#!/usr/bin/python3 # -*- coding:utf-8 -*- from bs4 import BeautifulSoup html = """ <html><head><title>The Dormouse's story</title></head> <body> <p class="title" name="dromouse"><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" class="sister" id="link1"><!-- Elsie --></a>, <a href="http://example.com/lacie" class="sister" id="link2">Lacie</a> and <a href="http://example.com/tillie" class="sister" id="link3">Tillie</a>; and they lived at the bottom of a well.</p> <p class="story">...</p> """ # 创建 Beautiful Soup 对象，指定lxml解析器 soup = BeautifulSoup(html, "lxml") # 输出方式为列表 print(soup.head.contents) print(soup.head.contents[0])
运行结果
[<title>The Dormouse's story</title>] <title>The Dormouse's story</title>
.children
它返回的不是一个列表，不过我们可以通过遍历获取所有的子节点。
#!/usr/bin/python3 # -*- coding:utf-8 -*- from bs4 import BeautifulSoup html = """ <html><head><title>The Dormouse's story</title></head> <body> <p class="title" name="dromouse"><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" class="sister" id="link1"><!-- Elsie --></a>, <a href="http://example.com/lacie" class="sister" id="link2">Lacie</a> and <a href="http://example.com/tillie" class="sister" id="link3">Tillie</a>; and they lived at the bottom of a well.</p> <p class="story">...</p> """ # 创建 Beautiful Soup 对象，指定lxml解析器 soup = BeautifulSoup(html, "lxml") # 输出方式为列表生成器对象 print(soup.head.children) # 通过遍历获取所有子节点 for child in soup.head.children: print(child)
运行结果
<list_iterator object at 0x008FF950> <title>The Dormouse's story</title>
2.所有子孙节点：.descendants属性
上面讲的.contents和.children属性仅包含Tag的直接子节点，.descendants属性可以对所有Tag的子孙节点进行递归循环，和children类似，我们也需要通过遍历的方式获取其中的内容。
#!/usr/bin/python3 # -*- coding:utf-8 -*- from bs4 import BeautifulSoup html = """ <html><head><title>The Dormouse's story</title></head> <body> <p class="title" name="dromouse"><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" class="sister" id="link1"><!-- Elsie --></a>, <a href="http://example.com/lacie" class="sister" id="link2">Lacie</a> and <a href="http://example.com/tillie" class="sister" id="link3">Tillie</a>; and they lived at the bottom of a well.</p> <p class="story">...</p> """ # 创建 Beautiful Soup 对象，指定lxml解析器 soup = BeautifulSoup(html, "lxml") # 输出方式为列表生成器对象 print(soup.head.descendants) # 通过遍历获取所有子孙节点 for child in soup.head.descendants: print(child)
运行结果
<generator object descendants at 0x00519AB0> <title>The Dormouse's story</title> The Dormouse's story
3.节点内容：.string属性
如果Tag只有一个NavigableString类型子节点，那么这个Tag可以使用.string得到子节点。如果一个Tag仅有一个子节点，那么这个Tab也可以使用.string方法，输出结果与当前唯一子节点的.string结果相同。
通俗点来讲就是：如果一个标签里面没有标签了，那么.string就会返回标签里面的内容。如果标签里面只有唯一的一个标签了，那么.string也会返回里面的内容。例如：
#!/usr/bin/python3 # -*- coding:utf-8 -*- from bs4 import BeautifulSoup html = """ <html><head><title>The Dormouse's story</title></head> <body> <p class="title" name="dromouse"><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" class="sister" id="link1"><!-- Elsie --></a>, <a href="http://example.com/lacie" class="sister" id="link2">Lacie</a> and <a href="http://example.com/tillie" class="sister" id="link3">Tillie</a>; and they lived at the bottom of a well.</p> <p class="story">...</p> """ # 创建 Beautiful Soup 对象，指定lxml解析器 soup = BeautifulSoup(html, "lxml") print(soup.head.string) print(soup.head.title.string)
运行结果
The Dormouse's story The Dormouse's story
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