由于BeautifulSoup库是对标签树功能的遍历集合，所以可以将所有的遍历功能分为上行遍历、下行遍历、平行遍历这三种遍历方式来组织。
QQ图片20200413225444.jpg
标签树的下行遍历
| 属性 | 说明 |
|---|---|
| .contents | 子节点的列表，将<tag>所有儿子节点存入列表 |
| .children | 子节点的迭代类型，与.contents类似，用于循环遍历儿子节点 |
| .descendants | 子孙节点的迭代类型，包含所有子孙节点，用于循环遍历 |
- 实例
#.contents 用法
>>> soup.head
<head><title>This is a python demo page</title></head>
>>> soup.head.contents
[<title>This is a python demo page</title>]
>>> soup.body.contents
['\n', <p class="title"><b>The demo python introduces several python courses.</b></p>, '\n', <p class="course">Python is a wonderful general-purpose programming language. You can learn Python from novice to professional by tracking the following courses:
<a class="py1" href="http://www.icourse163.org/course/BIT-268001" id="link1">Basic Python</a> and <a class="py2" href="http://www.icourse163.org/course/BIT-1001870001" id="link2">Advanced Python</a>.</p>, '\n']
#可以用len()函数获取body儿子节点的数量
>>> len(soup.body.contents)
5
>>>
#遍历儿子节点（.children）
>>> for child in soup.body.children:
print(child)
<p class="title"><b>The demo python introduces several python courses.</b></p>
<p class="course">Python is a wonderful general-purpose programming language. You can learn Python from novice to professional by tracking the following courses:
<a class="py1" href="http://www.icourse163.org/course/BIT-268001" id="link1">Basic Python</a> and <a class="py2" href="http://www.icourse163.org/course/BIT-1001870001" id="link2">Advanced Python</a>.</p>
>>>
标签树的上行遍历
| 属性 | 说明 |
|---|---|
| .parent | 节点的父亲标签 |
| .parents | 节点先辈标签的迭代类型，用于循环遍历先辈标签 |
- 用法实例
>>> soup = BeautifulSoup(demo, "html.parser")
>>> for parent in soup.a.parents:
if parent is None:
print(parent)
else:
print(parent.name)
p
body
html
[document]
>>>
在遍历一个标签的所有前辈标签时，会遍历到soup本身，而soup的先辈并不存在.name的信息。所以要进行区分。
标签树的平行遍历
| 属性 | 说明 |
|---|---|
| .next_sibling | 返回按照HTML文本顺序的下一个平行节点 |
| .previous_sibling | 返回按照HTML文本顺序的上一个平行节点 |
| .next_siblings | 迭代类型，返回按照HTML文本顺序的后续所有平行节点标签 |
| .previous_siblings | 迭代类型，返回按照HTML文本顺序的前续所有平行节点标签 |
QQ图片20200413224427.jpg
- 用法实例
>>> soup.a.next_sibling
' and '
>>> soup.a.next_sibling.next_sibling
<a class="py2" href="http://www.icourse163.org/course/BIT-1001870001" id="link2">Advanced Python</a>
>>> soup.a.previous_sibling
'Python is a wonderful general-purpose programming language. You can learn Python from novice to professional by tracking the following courses:\r\n'
>>> soup.a.previous_sibling.previous_sibling
>>> soup.a.parent
<p class="course">Python is a wonderful general-purpose programming language. You can learn Python from novice to professional by tracking the following courses:
<a class="py1" href="http://www.icourse163.org/course/BIT-268001" id="link1">Basic Python</a> and <a class="py2" href="http://www.icourse163.org/course/BIT-1001870001" id="link2">Advanced Python</a>.</p>
>>>
#遍历后续节点
>>> for sibling in soup.a.next_siblings:
print(sibling)
and
<a class="py2" href="http://www.icourse163.org/course/BIT-1001870001" id="link2">Advanced Python</a>
#遍历前续节点
>>> for sibling in soup.a.previous_siblings:
print(sibling)
Python is a wonderful general-purpose programming language. You can learn Python from novice to professional by tracking the following courses:
>>>
