'''
提取HTML中所有URL链接
'''
import requests
from bs4 import BeautifulSoup
import re
# r = requests.get("https://python123.io/ws/demo.html")
# demo = r.text
demo = """
<html><head><title>This is a python demo page</title></head>
<body>
<p class="title"><b>The demo python introduces several python courses.</b></p>
<p class="course">Python is a wonderful general-purpose programming language. You can learn Python from novice to professional by tracking the following courses:
<a href="http://www.icourse163.org/course/BIT-268001" class="py1" id="link1">Basic Python</a> and <a href="http://www.icourse163.org/course/BIT-1001870001" class="py2" id="link2">Advanced Python</a>.</p>
</body></html>
"""
"""
find_all(name, attrs, recursive, string, **kwargs)方法：
<tag>(..) 等价于 <tag>.find_all(..)
soup(..) 等价于 soup.find_all(..)
"""
soup = BeautifulSoup(demo, "html.parser")
for link in soup.find_all('a'): # 1、搜索到所有<a>标签
print(link.get("href")) # 2、解析<a>标签格式，提取href后的链接内容
print(soup.find_all('a')) # 查找<a>标签
'[<a class="py1" href="http://www.icourse163.org/course/BIT-268001" id="link1">Basic Python</a>, <a class="py2" href="http://www.icourse163.org/course/BIT-1001870001" id="link2">Advanced Python</a>]'
print(soup.find_all(['a', 'b'])) # 同时查找<a><b>标签
for tag in soup.find_all(True): # 获取所有标签
print(tag.name)
'''
html
head
title
body
p
b
p
a
a
'''
# 只显示以b开头的标签，包括<b>和<body>标签元素
for tag in soup.find_all(re.compile('b')): # 正则表达式查找以<b>开头的标签元素
print(tag.name)
print(soup.find_all('p', 'course')) # 返回<p>标签中，属性值为"course"的标签元素
print(soup.find_all(id = "link1")) # 返回属性中id域等于"link1"的标签元素
print(soup.find_all(id = re.compile("link"))) # 返回属性中id域以"link"开头的所有标签元素
print(soup.find_all(attrs={"class": "py1"}))