前言：
昨天把傳說中的BeautifulSoup4裝上了，還沒有裝好的童鞋，請看本人的上一篇博客：
Python3 Win7安裝 BeautifulSoup，按照裏面簡單的步驟就可以把BeautifulSoup裝上啦，很簡單的，表害怕
裝好BeautifulSoup4之後，就讓我們來好好享受這碗BeautifulSoup吧，哈哈
入門：
下面就來介紹一下BeautifulSoup吧，BeautifulSoup是一個可以從HTML或XML文件中提取數據的Python庫.它能夠通過你喜歡的轉換器實現慣用的文檔導航,查找,修改文檔的方式.Beautiful Soup會幫你節省數小時甚至數天的工作時間
在你知道有BeautifulSoup這貨之前，如果你從一個文本中提取出自己想要的東西，那麼估計你應該使用re模塊，但先在如果給你一個HTML文件讓你提取出一些關鍵信息，如果再使用re模塊，雖然也可以把信息提取出來，但是捏，你可能會絞盡腦汁苦思冥想查閱好多資料，現在，我們有了BeautifulSoup，一切變得超級簡單起來，對，就是這麼簡單
實踐：
學習bs4最好的還是查看bs4的官方文檔，有中文版的哦，猛點這裏官方文檔，看起來會很快，筆者花了大概一個下午的時間，把bs4的官方文檔看了一遍，順手也寫了寫裏面的示例程序，如果你沒多少時間的話，看看我下面的代碼，估計你會很快上手的，相信我 (*^_^*)
__author__ = 'MrChen'
from bs4 import BeautifulSoup
#這是示例
html_doc = """
<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="http://example.com/elsie" class="sister" id="link1">Elsie</a>,
<a href="http://example.com/lacie" class="sister" id="link2">Lacie</a> and
<a href="http://example.com/tillie" class="sister" id="link3">Tillie</a>;
and they lived at the bottom of a well.</p>
<p class="story">...</p>
"""
#初始化，實例化一個BeautifulSoup對象，參數可以是一個字符串，也可以是一個打開的文件比如open('mydoc.html')
soup = BeautifulSoup(html_doc)
print(soup.title)
#輸出：<title>The Dormouse's story</title>
print(soup.title.parent)
#輸出：<head><title>The Dormouse's story</title></head>
print(soup.title.parent.parent)
#輸出：
#<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 class="sister" href="http://example.com/elsie" id="link1">Elsie</a>,
#<a class="sister" href="http://example.com/lacie" id="link2">Lacie</a> and
#<a class="sister" href="http://example.com/tillie" id="link3">Tillie</a>;
#and they lived at the bottom of a well.</p>
#<p class="story">...</p>
#</body></html>
print(soup.title.name)
#輸出：title
print(soup.title.parent.name)
#輸出：head
print(soup.title.parent.parent.name)
#輸出：html
print(soup.p)
#輸出：<p class="title"><b>The Dormouse's story</b></p>
print(soup.p['class'])
#輸出：['title']
print(soup.a)
#輸出：<a class="sister" href="http://example.com/elsie" id="link1">Elsie</a>
print(soup.find_all('a'))
#輸出：
#[<a class="sister" href="http://example.com/elsie" id="link1">Elsie</a>,
# <a class="sister" href="http://example.com/lacie" id="link2">Lacie</a>,
# <a class="sister" href="http://example.com/tillie" id="link3">Tillie</a>]
print(soup.find(id = 'link3'))
#輸出：<a class="sister" href="http://example.com/tillie" id="link3">Tillie</a>
for link in soup.find_all('a'):
print(link.get('href'))
#輸出：
# http://example.com/elsie
# http://example.com/lacie
# http://example.com/tillie
print(soup.getText())
#輸出：
# The Dormouse's story
#
# The Dormouse's story
# Once upon a time there were three little sisters; and their names were
# Elsie,
# Lacie and
# Tillie;
# and they lived at the bottom of a well.
# ...
print('all tags : <<<<<<')
for tag in soup.find_all(True):
print(tag.name)
#輸出：
#html
#head
#title
#body
#p
#b
#p
#a
#a
#a
#p