Python，美汤，获取所有类名

给定一个 html 代码可以说：

 <div class="class1">
    <span class="class2">some text</span>
    <span class="class3">some text</span>
    <span class="class4">some text</span>
    </div>

如何检索所有类名？即：['class1','class2','class3','class4']

I tried:

soup.find_all(class_=True)

但它检索整个标签，然后我需要对字符串执行一些正则表达式

You can 对待每一个Tag实例被发现为字典 https://www.crummy.com/software/BeautifulSoup/bs4/doc/#attributes当涉及到检索属性时。注意class属性值将是list since class是一个特殊的“多值”属性 https://www.crummy.com/software/BeautifulSoup/bs4/doc/#multi-valued-attributes:

classes = []
for element in soup.find_all(class_=True):
    classes.extend(element["class"])

Or:

classes = [value
           for element in soup.find_all(class_=True)
           for value in element["class"]]

Demo:

from bs4 import BeautifulSoup

data = """
<div class="class1">
<span class="class2">some text</span>
<span class="class3">some text</span>
<span class="class4">some text</span>
</div>
"""

soup = BeautifulSoup(data, "html.parser")

classes = [value
           for element in soup.find_all(class_=True)
           for value in element["class"]]

print(classes)

# Returns
# ['class1', 'class2', 'class3', 'class4']