Python_网页爬虫

 1 import sys
 2 import multiprocessing
 3 import re
 4 import os
 5 import urllib.request as lib
 6
 7 def craw_links( url,depth,keyword,processed):
 8     ‘‘‘ url:the url to craw
 9         deth:the current depth to craw
10         keyword:the tuple of keywords to focus
11         pool:process pool
12     ‘‘‘
13
14     contents=[]
15     if url.startswith((‘htpp://‘,‘https://‘)):
16         if url not in processed:
17             #mark this url as processed
18             processed.append(url)
19         else:
20             #avoid prossing the same url again
21             return
22         print(‘Crawing ‘+url+‘...‘)
23         fp = lib.urlopen(url)
24         #python3 returns bytes,so need to decode
25         contents = fp.read()
26         contents_decoded = contents.decode(‘UTF-8‘)
27         fp.close()
28         pattern = ‘|‘.join(keyword)
29         #if this page contains certain keywords,save it to a file
30         flag = False
31         if pattern:
32             searched = re.search(pattern,contents_decoded)
33         else:
34             #if the keywords to filter is not given,save current page
35             flag = True
36         if flag or searched:
37             with open(‘craw\\‘+url.replace(‘:‘,‘_‘).replace(‘/‘,‘_‘),‘wb‘)  as fp:
38                 fp.write(contents)
39         #find all the links in the current page
40         links = re.findall(‘href="(.*?)"‘,contents_decoded)
41         #craw all links in the current page
42         for link in links:
43             #consider the relative path
44             if not link.startswith((‘http://‘,‘https://‘)):
45                 try:
46                     index=url.rindex(‘/‘)
47                     link = url[0:index+1]+link
48                 except:
49                     pass
50             if depth>0 and link.endswith((‘.htm‘,‘.html‘)):
51                 craw_links(link,depth-1,keyword,processed)
52
53 if __name__ == ‘__main__‘:
54     processed = []
55     keywords = (‘KeyWord1‘,‘KeyWord2‘)
56     if os.path.exists(‘craw‘) or not os.path.isdir(‘craw‘):
57         os.mkdir(‘craw‘)
58     craw_links(r‘http://docs.python.org/3/library/index.html‘,1,keywords,processed)