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！
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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 = """
The Dormouse's story
The Dormouse's story
Once upon a time there were three little sisters; and their names were
,
Lacie and
Tillie;
and they lived at the bottom of a well.
...
"""
# 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
[The Dormouse's story]
The Dormouse's story
.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 = """
The Dormouse's story
The Dormouse's story
Once upon a time there were three little sisters; and their names were
,
Lacie and
Tillie;
and they lived at the bottom of a well.
...
"""
# 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
The Dormouse's story
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 = """
The Dormouse's story
The Dormouse's story
Once upon a time there were three little sisters; and their names were
,
Lacie and
Tillie;
and they lived at the bottom of a well.
...
"""
# 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
The Dormouse's story
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 = """
The Dormouse's story
The Dormouse's story
Once upon a time there were three little sisters; and their names were
,
Lacie and
Tillie;
and they lived at the bottom of a well.
...
"""
# 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
看完了这篇文章，相信你对Python爬虫中遍历文档树的方法有了一定的了解，想了解更多相关知识，欢迎关注创新互联行业资讯频道，感谢各位的阅读！
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