一般写法

from lxml import  etree

html = '''
    <li class="tag_1">需要的内容1</li>
    <li class="tag_2">需要的内容2</li>
    <li class="tag_3">需要的内容3</li>
'''

selector =  etree.HTML(html )
contents  =  selector.xpath ( '//li[@class = "tag_1"]/text()')
print(contents)

输出：
D:\Python\venv\Scripts\python.exe D:/Python/venv/test9.py
['需要的内容1']

Process finished with exit code 0

starts-with()可以获取类似标签的信息。

from lxml import  etree

html = '''
    <li class="tag_1">需要的内容1</li>
    <li class="tag_2">需要的内容2</li>
    <li class="tag_3">需要的内容3</li>
'''

selector =  etree.HTML(html )
contents  =  selector.xpath ( '//li[starts-with(@class ,"tag")]/text()')
for  content  in  contents:
    print  (content)

输出：
D:\Python\venv\Scripts\python.exe D:/Python/venv/test9.py
需要的内容1
需要的内容2
需要的内容3

Process finished with exit code 0
**