CSS选择器
这是另一种与find_all()方法有异曲同工的查找方法，写CSS时，标签名不加任何修饰，类名前加.，id名前加#。
在这里我们也可以利用类似的方法来筛选元素，用到的方法是soup.select()，返回的类型是list。
（1）通过标签名查找
#!/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.select("title"))
print(soup.select("b"))
print(soup.select("a"))运行结果
[<title>The Dormouse's story</title>] [<b>The Dormouse's story</b>] [<a class="sister" href="http://example.com/elsie" id="link1"><!-- Elsie --></a>, <a class="sister" href="http://example.com/lacie" id="link2">Lacie</a>, <a class="sister" href="http://example.com/tillie" id="link3">Tillie</a>]
（2）通过类名查找
#!/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.select(".title"))运行结果
[<p class="title" name="dromouse"><b>The Dormouse's story</b></p>]
（3）通过id名查找
#!/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.select("#link1"))运行结果
[<p class="title" name="dromouse"><b>The Dormouse's story</b></p>]
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（4）组合查找
#!/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.select("p #link1"))运行结果
[<a class="sister" href="http://example.com/elsie" id="link1"><!-- Elsie --></a>]
（5）属性查找
查找时还可以加入属性元素，属性需要用中括号括起来，注意属性和标签属于同一节点，所以中间不能加空格，否则会无法匹配到。
#!/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.select("a[class='sister']"))运行结果
[<a class="sister" href="http://example.com/elsie" id="link1"><!-- Elsie --></a>, <a class="sister" href="http://example.com/lacie" id="link2">Lacie</a>, <a class="sister" href="http://example.com/tillie" id="link3">Tillie</a>]
同样，属性仍然可以与上述查找方式组合，不在同一节点的空格隔开，同一节点的不加空格。
#!/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.select("p a[class='sister']"))运行结果
[<a class="sister" href="http://example.com/elsie" id="link1"><!-- Elsie --></a>, <a class="sister" href="http://example.com/lacie" id="link2">Lacie</a>, <a class="sister" href="http://example.com/tillie" id="link3">Tillie</a>]
（6）获取内容
以上的select()方法返回的结果都是列表形式，可以遍历形式输出，然后用get_text()方法来获取它的内容。
#!/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")
print(soup.select("p a[class='sister']"))
for item in soup.select("p a[class='sister']"):
print(item.get_text())运行结果
[<a class="sister" href="http://example.com/elsie" id="link1"><!-- Elsie --></a>, <a class="sister" href="http://example.com/lacie" id="link2">Lacie</a>, <a class="sister" href="http://example.com/tillie" id="link3"> Tillie</a>] Lacie Tillie
注意：<!-- Elsie -->为注释内容，未输出
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