beautifulsoup4教程（四）css选择器

beautifulsoup4教程（一）基础知识和第一个爬虫

 beautifulsoup4教程（二）bs4中四大对象

 beautifulsoup4教程（三）遍历和搜索文档树

 beautifulsoup4教程（四）css选择器

六、CSS选择器

6.1 通过标签名查找

print soup.select('title')
print soup.select('a')
print soup.select('b')

result:
[<title>The Dormouse's story</title>]
[<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>]
[<b>The Dormouse's story</b>]

6.2 通过类名查找

print soup.select('.story')

result:
[<p class="story">Once upon a time there were three little sisters; and their names were\n<a class="sister" href="http://example.com/elsie" id="link1"><!-- Elsie --></a>,\n<a class="sister" href="http://example.com/lacie" id="link2">Lacie</a> and\n<a class="sister" href="http://example.com/tillie" id="link3">Tillie</a>;\nand they lived at the bottom of a well.</p>, <p class="story">...</p>]

6.3 通过id名查找

print soup.select('#link1')

result:
print soup.select('#link1')

6.4 组合查找

多个过滤条件需要用空格隔开,从前往后是逐层筛选，选择器作用的不是同一个结点。

print soup.select('p #link1')
print soup.select('a #link1')

result:
[<a class="sister" href="http://example.com/elsie" id="link1"><!-- Elsie --></a>]
[]

通过下面这种方式会更好理解

print soup.select('p >#link1')
print soup.select('a >#link1')

result:
[<a class="sister" href="http://example.com/elsie" id="link1"><!-- Elsie --></a>]
[]

6.5 属性查找

print soup.select('p >a')
print soup.select('p >a[href="http://example.com/tillie"]')

result:
[<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>]
[<a class="sister" href="http://example.com/tillie" id="link3">Tillie</a>]

6.6 列表迭代

通过上述方法返回的都是列表，是可迭代对象。

print soup.select('p >a')
print type(soup.select('p >a'))
print "===="
print soup.select('p >a')[0]
print "===="
for a in soup.select('p >a'):
    print a
    
result:
[<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>]
<type 'list'>
====
<a class="sister" href="http://example.com/elsie" id="link1"><!-- Elsie --></a>
====
<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>