爬蟲實踐

1.URL爬取

　　爬取一個站點的全部URL，大概有如下步驟：

　　1.肯定好要爬取的入口連接。

　　2.根據需求構建好連接提取的正則表達式。

　　3.模擬成瀏覽器並爬取對應的網頁。

　　4.根據2中的正則表達式提取出該網頁中包含的連接。

　　5.過濾重複的連接。

　　6.後續操做，打印連接或存到文檔上。

　　這裏以獲取 https://blog.csdn.net/ 網頁上的連接爲例，代碼以下：

 1 import re
 2 import requests
 3 
 4 def get_url(master_url):
 5     header = {
 6         'Accept':'text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,image/apng,*/*;q=0.8',
 7         'Accept-Encoding':'gzip, deflate, br',
 8         'Accept-Language':'zh-CN,zh;q=0.9',
 9         'Cache-Control':'max-age=0',
10         'Connection':'keep-alive',
11         'Cookie':'uuid_tt_dd=10_20323105120-1520037625308-307643; __yadk_uid=mUVMU1b33VoUXoijSenERzS8A3dUIPpA; Hm_lvt_6bcd52f51e9b3dce32bec4a3997715ac=1521360621,1521381435,1521382138,1521382832; dc_session_id=10_1521941284960.535471; TY_SESSION_ID=7f1313b8-2155-4c40-8161-04981fa07661; ADHOC_MEMBERSHIP_CLIENT_ID1.0=51691551-e0e9-3a5e-7c5b-56b7c3f55f24; dc_tos=p64hf6',
12         'Host':'blog.csdn.net',
13         'Upgrade-Insecure-Requests':'1',
14         'User-Agent':'Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/64.0.3282.186 Safari/537.36'
15     }
16     patten = r'https?://[^\s]*'
17     requests.Encoding = 'utf-8'
18     response = requests.get(url=master_url,headers=header)
19     text = response.text
20     result = re.findall(patten,text)
21     result = list(set(result))
22     url_list = []
23     for i in result:
24         url_list.append(i.strip('"'))#過濾掉url中的"
25     return url_list
26 
27 url = get_url("https://blog.csdn.net/")
28 print(url,len(url))
29 for u in url:
30     with open('csdn_url.txt','a+') as f:
31         f.write(u)
32         f.write('\n')

打印結果：

2.糗事百科

　　具體思路以下：

　　1.分析網頁間的網址規律，構建網址變量，並能夠經過for循環實現多頁面內容的爬取。

　　2.構建函數，提取用戶以及用戶的內容。

　　3.獲取URL，調用函數，獲取到段子。

 1 import requests
 2 from lxml import html
 3 
 4 def get_content(page):
 5     header = {
 6         'Accept':'text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,image/apng,*/*;q=0.8',
 7         'Accept-Encoding':'gzip, deflate, br',
 8         'Accept-Language':'zh-CN,zh;q=0.9',
 9         'Cache-Control':'max-age=0',
10         'Connection':'keep-alive',
11         'Cookie':'_xsrf=2|bc420b81|bc50e4d023b121bfcd6b2f748ee010e1|1521947174; Hm_lvt_2670efbdd59c7e3ed3749b458cafaa37=1521947176; Hm_lpvt_2670efbdd59c7e3ed3749b458cafaa37=1521947176',
12         'Host':'www.qiushibaike.com',
13         'If-None-Match':"91ded28d6f949ba8ab7ac47e3e3ce35bfa04d280",
14         'Upgrade-Insecure-Requests':'1',
15         'User-Agent':'Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/64.0.3282.186 Safari/537.36',
16     }
17     requests.Encoding='utf-8'
18     url_='https://www.qiushibaike.com/8hr/page/%s/'%page
19     response = requests.get(url=url_,headers=header)
20     selector = html.fromstring(response.content)
21     users = selector.xpath('//*[@id="content-left"]/div/div[1]/a[2]/h2/text()')
22     contents = []
23     #獲取每條段子的所有內容
24     for x in range(1,25):
25         content = ''
26         try:
27             content_list = selector.xpath('//*[@id="content-left"]/div[%s]/a/div/span/text()'%x)
28             if isinstance(content_list,list):
29                 for c in content_list:
30                     content += c.strip('\n')
31             else:
32                 content = content_list
33             contents.append(content)
34         except:
35             raise '該頁沒有25條段子'
36     result = {}
37     i = 0
38     for user in users:
39         result[user.strip('\n')] = contents[i].strip('\n')
40         i += 1
41     return result
42 if __name__ == '__main__':
43     for i in range(1,5):
44         get_content(i)

打印結果：

 3.微信公衆號文章爬取

搜狗的微信搜索平臺 http://weixin.sogou.com/ ，搜索Python，經過URL http://weixin.sogou.com/weixin?query=python&type=2&page=2&ie=utf8 分析搜索關鍵詞爲query，分頁爲page，爲此已經能夠構造出這次爬蟲的主URL。

接下來分析文章的URL：

能夠獲取到文章URL的xpath：//*[@class="news-box"] /ul/li/div[2]/h3/a/@href

這裏大量訪問很容易被封IP，全部咱們在requests請求中添加了代理參數 proxies

 1 import requests
 2 from lxml import html
 3 import random
 4 
 5 def get_weixin(page):
 6     url = "http://weixin.sogou.com/weixin?query=python&type=2&page=%s&ie=utf8"%page
 7     header = {
 8         'Accept':'text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,image/apng,*/*;q=0.8',
 9         'Accept-Encoding':'gzip, deflate',
10         'Accept-Language':'zh-CN,zh;q=0.9',
11         'Cache-Control':'max-age=0',
12         'Connection':'keep-alive',
13         'Cookie':'SUV=1520147372713631; SMYUV=1520147372713157; UM_distinctid=161efd81d192bd-0b97d2781c94ca-454c062c-144000-161efd81d1b559; ABTEST=0|1521983141|v1; IPLOC=CN4403; SUID=CADF1E742423910A000000005AB79EA5; SUID=CADF1E743020910A000000005AB79EA5; weixinIndexVisited=1; sct=1; SNUID=E3F7375C282C40157F7CE81D2941A5AD; JSESSIONID=aaaXYaqQLrCiqei2IKOiw',
14         'Host':'weixin.sogou.com',
15         'Referer':url,
16         'Upgrade-Insecure-Requests':'1',
17         'User-Agent':'Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/64.0.3282.186 Safari/537.3'
18     }
19     requests.Encoding='utf-8'
20     proxy_list = get_proxy()
21     #使用代理並嘗試請求，直到成功
22     while True:
23         proxy_ip = random.choice(proxy_list)
24         try:
25             response = requests.get(url=url,headers=header,proxies=proxy_ip).content
26             selector = html.fromstring(response)
27             content_url = selector.xpath('//*[@class="news-box"] /ul/li/div[2]/h3/a/@href')
28             break
29         except:
30             continue
31     return content_url
32 
33 def get_proxy(url='http://api.xicidaili.com'):
34     requests.Encoding='utf-8'
35     header = {
36         'Accept':'text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,image/apng,*/*;q=0.8',
37         'Accept-Encoding':'gzip, deflate',
38         'Accept-Language':'zh-CN,zh;q=0.9',
39         'Cache-Control':'max-age=0',
40         'Connection':'keep-alive',
41         'Cookie':'_free_proxy_session=BAh7B0kiD3Nlc3Npb25faWQGOgZFVEkiJTE1MWEzNGE0MzE1ODA3M2I3MDFkN2RhYjQ4MzZmODgzBjsAVEkiEF9jc3JmX3Rva2VuBjsARkkiMWZNM0MrZ0xic09JajRmVGpIUDB5Q29aSSs3SlAzSTM4TlZsLzNOKzVaQkE9BjsARg%3D%3D--eb08c6dcb3096d2d2c5a4bc77ce8dad2480268bd; Hm_lvt_0cf76c77469e965d2957f0553e6ecf59=1521984682; Hm_lpvt_0cf76c77469e965d2957f0553e6ecf59=1521984778',
42         'Host':'www.xicidaili.com',
43         'If-None-Match':'W/"df77cf304c5ba860bd40d8890267467b"',
44         'Referer':'http://www.xicidaili.com/api',
45         'Upgrade-Insecure-Requests':'1',
46         'User-Agent':'Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/64.0.3282.186 Safari/537.3'
47     }
48     response = requests.get(url=url,headers=header).content
49     selector = html.fromstring(response)
50     proxy_list = selector.xpath('//*[@id="ip_list"]/tr/td[2]/text()')
51     return proxy_list
52 
53 
54 if __name__ == '__main__':
55     for i in range(1,10):
56         print(get_weixin(i))

經過這個爬蟲，學會了如何使用代理IP請求。