Beautifulsoup return 属性列表 "class" 而其他属性的值

Question

Beautifulsoup 方便 html 在 python 中解析，下面的代码结果 cofuse me.

from bs4 import BeautifulSoup
tr ="""
<table>
    <tr class="passed" id="row1"><td>t1</td></tr>
    <tr class="failed" id="row2"><td>t2</td></tr>
</table>
"""
table = BeautifulSoup(tr,"html.parser")
for row in table.findAll("tr"):
    print row["class"]
    print row["id"]

结果：

[u'passed']
row1
[u'failed']
row2

为什么属性 class returns 为数组？而 id 是正常值 ?

beautifulsoup4-4.5.0 与 python 2.7

一起使用

Answer 1

class is a special multi-valued attribute 在 BeautifulSoup:

HTML 4 defines a few attributes that can have multiple values. HTML 5 removes a couple of them, but defines a few more. The most common multi-valued attribute is class (that is, a tag can have more than one CSS class)

有时，这是一个难以处理的问题 - 例如，当您想要将正则表达式应用于整个 class 属性值时：

你可以，但我不建议这样做。

Answer 2

因为元素可能有多个类.

考虑这个例子：

从 bs4 导入 BeautifulSoup

tr ="""
<table>
    <tr class="passed a b c" id="row1"><td>t1</td></tr>
    <tr class="failed" id="row2"><td>t2</td></tr>
</table>
"""
table = BeautifulSoup(tr,"html.parser")
for row in table.findAll("tr"):
    print row["class"]
    print row["id"]

['passed', 'a', 'b', 'c']
row1
['failed']
row2

Beautifulsoup return 属性列表 "class" 而其他属性的值

Beautifulsoup return list for attribute "class" while value for other attribute

python

beautifulsoup

html-parsing