Example of web crawler in python core programming, python core programming Crawler

Example of web crawler in python core programming, python core programming Crawler

  1 #!/usr/bin/env python  2   3 import cStringIO                    #  4 import formatter                    #  5 from htmllib import HTMLParser         # We use various classes in these modules for parsing HTML.  6 import httplib                        # We only need an exception from this module  7 import os                            # This provides various file system functions  8 import sys                            # We are just using argv for command-line arguments  9 import urllib                        # We only need the urlretrieve()function for downloading Web pages 10 import urlparse                        # We use the urlparse()and urljoin()functions for URL manipulation 11  12 class Retriever(object): 13     __slots__ = ('url','file') 14      15     def __init__(self,url): 16         self.url, self.file = self.get_file(url) 17          18     def get_file(self, url, default='index.html'): 19         'Create usable local filename from URL' 20         parsed = urlparse.urlparse(url)                     # ParseResult(scheme='http', netloc='www.baidu.com', path='', params='', query='', fragment='') 21         host = parsed.netloc.split('@')[-1].split(':')[0]    # 'www.baidu.com' 22         filepath = '%s%s' % (host,parsed.path)                # 'www.baidu.com' 23         if not os.path.splitext(parsed.path)[1]:            # '' 24             filepath = os.path.join(filepath, default)        # 'www.baidu.com\\index.html' 25         linkdir = os.path.dirname(filepath)                    # 'www.baidu.com' 26         if not os.path.isdir(linkdir):                        # False 27             if os.path.exists(linkdir):                        # False 28                 os.unlink(linkdir)                             29             os.makedirs(linkdir)                            # make a directory named by link directory on the hard disc 30         return url, filepath 31          32     def download(self): 33         'Download URL to specific name file' 34         try: 35             retval = urllib.urlretrieve(self.url, self.file) 36         except (IOError, httplib.InvalidURL) as e: 37             retval = (('*** ERROR:bad URL "%s": %s' % (self.url,e)),) 38         return retval 39          40     def parse_links(self): 41         'Parse out the links found in downloaded HTML file' 42         f = open(self.file, 'r') 43         data = f.read() 44         f.close() 45         parser = HTMLParser(formatter.AbstractFormatter(formatter.DumbWriter(cStringIO.StringIO()))) 46         parser.feed(data) 47         parser.close() 48         return parser.anchorlist 49          50 class Crawler(object): 51     count = 0                                                # the number of objects downloaded from the internet 52      53     def __init__(self, url): 54         self.q = [url]                                        # a queue of links to download 55         self.seen = set()                                    # a set containing all the links that we have seen(downloaded) already 56         parsed = urlparse.urlparse(url) 57         host = parsed.netloc.split('@')[-1].split(':')[0] 58         self.dom = '.'.join(host.split('.')[-2:])            # 'b.a.i.d.u' 59  60     def get_page(self, url, media=False): 61         'Download page & parse links, add to queue if nec' 62         r = Retriever(url) 63         fname = r.download()[0]                                # 'www.baidu.com\\index.html' 64         if fname[0] == '*':                                    # 'w' 65             print fname, '... skipping parse' 66             return 67         Crawler.count += 1                                    # 1 68         print '\n(', Crawler.count, ')'                        # (1) 69         print 'URL:', url                                    # URL: http://www.baidu.com 70         print 'FILE:', fname                                # FILE: www.baidu.com\\index.html 71         self.seen.add(url)                                    # set(['http://www.baidu.com']) 72         ftype = os.path.splitext(fname)[1]                    # '.html' 73         if ftype not in ('.htm', '.html'):                    # False 74             return 75              76         for link in r.parse_links(): 77             if link.startswith('mailto:'):                    # False 78                 print '... discarded, mailto link' 79                 continue 80             if not media:                                    # False 81                 ftype = os.path.splitext(link)[1] 82                 if ftype in ('.mp3','.mp4','.m4v','.wav'): 83                     print '... discarded, media file' 84                     continue 85             if not link.startswith('http://'):                # False 86                 link = urlparse.urljoin(url, link) 87             print '*', link, 88             if link not in self.seen:                        # True 89                 if self.dom not in link:                    # False 90                     print '... discarded, not in domain' 91                 else: 92                     if link not in self.q: 93                         self.q.append(link) 94                         print '... new, added to Q' 95                     else: 96                         print '... discarded, already in Q' 97             else: 98                 print '... discarded, already processed' 99                 100     def go(self, media=False):101         'Process next page in queue (if any)'102         while self.q:103             url = self.q.pop()104             self.get_page(url, media)105             106 def main():107         if len(sys.argv) > 1:108             url = sys.argv[1]109         else:110             try:111                 url = raw_input('Enter starting URL:')112             except(KeyboardInterrupt, EOFError):113                 url = ''114         if not url:115             return116         if not url.startswith('http://') and not url.startswith('ftp://'):117             url = 'http://%s/' % url118         robot = Crawler(url)119         robot.go()120         121 if __name__ == '__main__':122         main()

What is the focus of python learning? With the second version of python core programming, how can this book be used better?

Python is the fourth-generation programming language. It has a low entry threshold and a quick start.
At the beginning, to cultivate interest, you can write some small script examples, such as batch file processing and regular expression matching;
Other network applications can also be involved.
To be more in-depth, you need to understand object-oriented.
The core programming book is a collection of online python Forum results, more practical, you can learn from examples.
Then you can look for popular python frameworks and python open-source projects to see the source code.
But in general, python has a bottleneck in efficiency. Generally, it plays the role of script cohesion and batch processing in large systems.

In the example at the beginning of chapter 2 of Python core programming, what is the appending of the open function mode? Why is the print content not displayed?

What do you want to do?

If you want
'Fatal error: invalid input! '

If this string is written to a file, you must use the 'W' parameter in the first sentence to create a file. You cannot create a file directly using 'A'. You can only open an existing file and add new content to it.

If the program runs smoothly, A mylog.txt file appears under the folder you specified, containing the content you print in.

The role of B is used together with the pickle module. It is recommended that you check the pickle part in the python manual. After reading it, you will know the role of B.