python爬取网页数据


一、利用webbrowser.open()打开一个网站:

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>>> import webbrowser
>>> webbrowser. open ( 'http://i.firefoxchina.cn/?from=worldindex' )
True

实例:使用脚本打开一个网页。

所有Python程序的第一行都应以#!python开头,它告诉计算机想让Python来执行这个程序。(我没带这行试了试,也可以,可能这是一种规范吧)

1.从sys.argv读取命令行参数:打开一个新的文件编辑器窗口,输入下面的代码,将其保存为map.py。

2.读取剪贴板内容:

3.调用webbrowser.open()函数打开外部浏览:

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#! python3
import webbrowser, sys, pyperclip
if len (sys.argv) > 1 :
  mapAddress = ''.join(sys.argv[ 1 :])
else :
  mapAddress = pyperclip.paste()
webbrowser. open ( 'http://map.baidu.com/?newmap=1&ie=utf-8&s=s%26wd%3D' + mapAddress

注:不清楚sys.argv用法的,请参考这里;不清楚.join()用法的,请参考这里。sys.argv是字符串的列表,所以将它传递给join()方法返回一个字符串。

好了,现在选中'天安门广场'这几个字并复制,然后到桌面双击你的程序。当然你也可以在命令行找到你的程序,然后输入地点。

二、用requests模块从Web下载文件:requests模块不是Python自带的,通过命令行运行pip install request安装。没翻墙是很难安装成功的,手动安装可以参考这里

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>>> import requests
>>> res = requests.get( 'http://i.firefoxchina.cn/?from=worldindex' ) #向get中传入一个网址
>>> type (res) #响应对象
< class 'requests.models.Response' >
>>> print (res.status_code) #响应码
200
>>> res.text #返回的文本

requests中查看网上下载的文件内容的方法还有很多,如果以后的博客用的到,会做说明,在此不再一一介绍。在下载文件的过程中,用raise_for_status()方法可以确保下载确实成功,然后再让程序继续做其他事情。

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import requests
try :
  res.raise_for_status()
except Exception as exc:
  print ( 'There was a problem: %s' % (exc))

三、将下载的文件保存到本地:

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>>> import requests
>>> res = requests.get( 'http://tech.firefox.sina.com/17/0820/10/6DKQALVRW5JHGE1I.html##0-tsina-1-13074-397232819ff9a47a7b7e80a40613cfe1' )
>>> res.raise_for_status()
>>> file = open ( '1.txt' , 'wb' ) #以写二进制模式打开文件,目的是保存文本中的“Unicode编码”
>>> for word in res.iter_content( 100000 ): #<span class="fontstyle0"><span class="fontstyle0">iter_content()</span><span class="fontstyle1">方法在循环的每次迭代中返回一段</span><span class="fontstyle0">bytes</span><span class="fontstyle1">数据</span><span class="fontstyle1">类型的内容,你需要指定其包含的字节数</span></span>
  file .write(word)
  
  
16997
>>> file .close()

四、用BeautifulSoup模块解析HTML:在命令行中用pip install beautifulsoup4安装它。
1.bs4.BeautifulSoup()函数可以解析HTML网站链接requests.get(),也可以解析本地保存的HTML文件,直接open()一个本地HTML页面。

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>>> import requests, bs4
>>> res = requests.get( 'http://i.firefoxchina.cn/?from=worldindex' )
>>> res.raise_for_status()
>>> soup = bs4.BeautifulSoup(res.text)
  
Warning ( from warnings module):
  File "C:\Users\King\AppData\Local\Programs\Python\Python36-32\lib\site-packages\beautifulsoup4-4.6.0-py3.6.egg\bs4\__init__.py" , line 181
  markup_type = markup_type))
UserWarning: No parser was explicitly specified, so I 'm using the best available HTML parser for this system ("html.parser"). This usually isn' t a problem, but if you run this code on another system, or in a different virtual environment, it may use a different parser and behave differently.
  
The code that caused this warning is on line 1 of the file <string>. To get rid of this warning, change code that looks like this:
  
  BeautifulSoup(YOUR_MARKUP})
  
to this:
  
  BeautifulSoup(YOUR_MARKUP, "html.parser" )
  
>>> soup = bs4.BeautifulSoup(res.text, 'html.parser' )
>>> type (soup)
< class 'bs4.BeautifulSoup' >

我这里有错误提示,所以加了第二个参数。

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>>> import bs4
>>> html = open ( 'C:\\Users\\King\\Desktop\\1.htm' )
>>> exampleSoup = bs4.BeautifulSoup(html)
>>> exampleSoup = bs4.BeautifulSoup(html, 'html.parser' )
>>> type (exampleSoup)
< class 'bs4.BeautifulSoup' >

2.用select()方法寻找元素:需传入一个字符串作为CSS“选择器”来取得Web页面相应元素,例如:
soup.select('div'):所有名为<div>的元素;

soup.select('#author'):带有id属性为author的元素;

soup.select('.notice'):所有使用CSS class属性名为notice的元素;

soup.select('div span'):所有在<div>元素之内的<span>元素;

soup.select('input[name]'):所有名为<input>并有一个name属性,其值无所谓的元素;

soup.select('input[type="button"]'):所有名为<input>并有一个type属性,其值为button的元素。

想查看更多的解析器,请参看这里。

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>>> import requests, bs4
>>> res = requests.get( 'http://i.firefoxchina.cn/?from=worldindex' )
>>> res.raise_for_status()
>>> soup = bs4.BeautifulSoup(res.text, 'html.parser' )
>>> author = soup.select( '#author' )
>>> print (author)
[]
>>> type (author)
< class 'list' >
>>> link = soup.select( 'link ' )
>>> print (link)
[<link href = "css/mozMainStyle-min.css?v=20170705" rel = "external nofollow" rel = "external nofollow" rel = "stylesheet" type = "text/css" / >, <link href = " " id=" rel = "external nofollow" rel = "external nofollow" rel = "external nofollow" moz - skin " rel=" stylesheet " type=" text / css "/>, <link href=" " id=" rel = "external nofollow" rel = "external nofollow" rel = "external nofollow" moz - dir " rel=" stylesheet " type=" text / css "/>, <link href=" " id=" rel = "external nofollow" rel = "external nofollow" rel = "external nofollow" moz - ver " rel=" stylesheet " type=" text / css" / >]
>>> type (link)
< class 'list' >
>>> len (link)
4
>>> type (link[ 0 ])
< class 'bs4.element.Tag' >
>>> link[ 0 ]
<link href = "css/mozMainStyle-min.css?v=20170705" rel = "external nofollow" rel = "external nofollow" rel = "stylesheet" type = "text/css" / >
>>> link[ 0 ].attrs
{ 'rel' : [ 'stylesheet' ], 'type' : 'text/css' , 'href' : 'css/mozMainStyle-min.css?v=20170705' }

 3.通过元素的属性获取数据:接着上面的代码写。

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>>> link[ 0 ].get( 'href' )
'css / mozMainStyle - min .css?v = 20170705
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