;a class="sister" href="http://example.com/elsie" id="link1"><!-- Elsie --></a>
Elsie
<class 'bs4.element.Comment'>
a标签里的内容实际上是注释，但是如果我们利用.string来输出它的内容时，注释符号已经去掉了。
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 -*-
__author__ = 'mayi'
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 -*-
__author__ = 'mayi'
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 -*-
__author__ = 'mayi'
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>
&