find_all() 函数是 BeautifulSoup 库中的函数，用于在 HTML 或 XML 文档中查找所有匹配给定标签的元素。该函数接受一个参数，即要查找的标签名，并返回一个包含所有匹配元素的列表。
用法:
_all(name, attrs, recursive, string, limit, **kwargs)
其中:
- name: 可以是标签名，字符串，正则表达式，列表
- attrs: 可以是字典，字符串
- recursive: 递归查找,默认True
- string: 查找文本
- limit: 限制查找数量
示例：
from bs4 import BeautifulSoup
html = """<html>
<head>
<title>The Dormouse's story</title>
</head>
<body>
<p class="title">
<b>The Dormouse's story</b>
</p>
<p class="story">Once upon a time there were three little sisters; and their names were
<a href="/elsie" class="sister" id="link1">Elsie</a>,
<a href="/lacie" class="sister" id="link2">Lacie</a> and
<a href="/tillie" class="sister" id="link3">Tillie</a>;
and they lived at the bottom of a well.</p>
<p class="story">...</p>
</body>
</html>
"""
soup = BeautifulSoup(html,'lxml')
soup.find_all('a')
#结果是返回所有的<a>标签