bs4的findAll传入双class属性字典时仅返回green标签的问题排查

• Python原生字典不支持重复键名，代码中属性字典两次声明class键，后定义的键值会覆盖前值，最终传入查询方法的匹配条件仅保留单个class规则，自然无法同时匹配两类标签。
• 额外注意：class是Python语言保留关键字，直接在find/find_all方法中传class=参数会触发语法错误，bs4专门提供了class_别名参数适配这个场景；同时class本身是HTML多值属性，直接给字典传单值的逻辑，不适用多类名匹配需求。

两种常用写法都可以实现同时匹配class为green、red的span标签：

• 方案1：用class_参数直接传值列表，写法最简洁

namelist = bsObj.find_all('span', class_=['green', 'red'])

• 方案2：用正则匹配class属性值，适合更复杂的模糊匹配场景

import re
namelist = bsObj.find_all('span', {'class': re.compile(r'^(green|red)$')})

from urllib.request import urlopen
from urllib.error import HTTPError
from bs4 import BeautifulSoup

URL = 'https://www.pythonscraping.com/pages/warandpeace.html'

def get_title(URL):
    try:
        html = urlopen(URL)
    except HTTPError as e:
        return None
    try:
        bsObj = BeautifulSoup(html.read(), 'html.parser')
        namelist = bsObj.find_all('span', class_=['green', 'red'])
    except AttributeError as e:
        return None
    return namelist

namelist = get_title(URL)
if namelist == None:
    print('we cant take title')
else:
    for name in namelist:
        print(name.get_text())

内容的提问来源于stack exchange，提问作者Platothecynic