python爬取網頁數據


一、利用webbrowser.open()打開一個網站:

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

實例:使用腳本打開一個網頁。

所有Python程序的第一行都應以#!python開頭,它告訴計算機想讓Python來執行這個程序。(我沒帶這行試了試,也可以,可能這是一種規范吧)

1.從sys.argv讀取命令行參數:打開一個新的文件編輯器窗口,輸入下面的代碼,將其保存為map.py。

2.讀取剪貼板內容:

3.調用webbrowser.open()函數打開外部瀏覽:

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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,請參考這里;不清楚.join()用法的,請參考這里。sys.argv是字符串的列表,所以將它傳遞給join()方法返回一個字符串。

好了,現在選中'天安門廣場'這幾個字並復制,然后到桌面雙擊你的程序。當然你也可以在命令行找到你的程序,然后輸入地點。

二、用requests模塊從Web下載文件:requests模塊不是Python自帶的,通過命令行運行pip install request安裝。沒翻牆是很難安裝成功的,手動安裝可以參考這里

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>>> import requests
>>> res = requests.get( 'http://i.firefoxchina.cn/?from=worldindex' ) #向get中傳入一個網址
>>> type (res) #響應對象
< class 'requests.models.Response' >
>>> print (res.status_code) #響應碼
200
>>> res.text #返回的文本

requests中查看網上下載的文件內容的方法還有很多,如果以后的博客用的到,會做說明,在此不再一一介紹。在下載文件的過程中,用raise_for_status()方法可以確保下載確實成功,然后再讓程序繼續做其他事情。

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

三、將下載的文件保存到本地:

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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' ) #以寫二進制模式打開文件,目的是保存文本中的“Unicode編碼”
>>> for word in res.iter_content( 100000 ): #<span class="fontstyle0"><span class="fontstyle0">iter_content()</span><span class="fontstyle1">方法在循環的每次迭代中返回一段</span><span class="fontstyle0">bytes</span><span class="fontstyle1">數據</span><span class="fontstyle1">類型的內容,你需要指定其包含的字節數</span></span>
  file .write(word)
  
  
16997
>>> file .close()

四、用BeautifulSoup模塊解析HTML:在命令行中用pip install beautifulsoup4安裝它。
1.bs4.BeautifulSoup()函數可以解析HTML網站鏈接requests.get(),也可以解析本地保存的HTML文件,直接open()一個本地HTML頁面。

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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' >

我這里有錯誤提示,所以加了第二個參數。

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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()方法尋找元素:需傳入一個字符串作為CSS“選擇器”來取得Web頁面相應元素,例如:
soup.select('div'):所有名為<div>的元素;

soup.select('#author'):帶有id屬性為author的元素;

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

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

soup.select('input[name]'):所有名為<input>並有一個name屬性,其值無所謂的元素;

soup.select('input[type="button"]'):所有名為<input>並有一個type屬性,其值為button的元素。

想查看更多的解析器,請參看這里。

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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.通過元素的屬性獲取數據:接着上面的代碼寫。

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