Simple Crawler Using Python

crawler.py

"""
	crawler.py
	web link crawler
	Nov 3rd 2012 saturday night insomnia coding session
	Fauzan Erich Emmerling
	erich@emfeld.com
"""

import re
from urllib2 import urlopen

links = []
root_url = 'http://www.google.com/'  # sample root url only. Use any links you wish


def extract_links(url):
    counter = 0  # use this to count the links found in url
    anchor_pattern = '<a'  # search for this to ensure that you are checking an anchor link element
    href_pattern = 'href="http:'  # search this for easier link extraction

    print 'Crawl links in ' + url

    try:
        html_data = urlopen(url)
        lines_list = html_data.readlines()
        for line in lines_list:
            anchor_element = re.search(anchor_pattern, line)
            if anchor_element:
                attributes = line.split(' ')
                for attribute in attributes:
                    href_link = re.search(href_pattern, attribute)
                    if href_link:
                        link = attribute.split('"')
                        if len(links) == 0:  # if the list is empty, append the component
                            links.append(link[1])
                            counter = counter + 1
                        else:
                            if not link[1] in links:  # if the list is not empty, check if link already existed
                                links.append(link[1])
                                counter = counter + 1
        print str(counter) + ' links found in ' + url
    except:
        print 'link inaccessible'

extract_links(root_url)  # crawl base page

for link in links:  # crawl all links other than base page
    if link != root_url:
        extract_links(link)

for link in links:  # display all links found in the website
    print link

print str(len(links)) + ' total links found in the website'