Simple Web Spider in Python

Opening an network connection with urllib2

import urllib2

request = urllib2.Request("http://www.volkskrant.nl/")
f=urllib2.urlopen(request)

print f.geturl()
print f.info()
print f.read()

Some sites require that you set the "User-Agent" header.

import urllib2

request = urllib2.Request("http://www.volkskrant.nl/")
request.add_header("User-Agent", "Mozilla/5.0 (X11; U; Linux x86_64; fr; rv:1.9.1.5) Gecko/20091109 Ubuntu/9.10 (karmic) Firefox/3.5.5")
f=urllib2.urlopen(request)

Get the URL of all images on a page and download them in a folder

import urllib2, urlparse, html5lib, lxml
from lxml.cssselect import CSSSelector

request = urllib2.Request("http://www.volkskrant.nl/")
request.add_header("User-Agent", "Mozilla/5.0 (X11; U; Linux x86_64; fr; rv:1.9.1.5) Gecko/20091109 Ubuntu/9.10 (karmic) Firefox/3.5.5")
f=urllib2.urlopen(request)

# f.geturl(), f.info()

parser = html5lib.HTMLParser(tree=html5lib.treebuilders.getTreeBuilder("lxml"), namespaceHTMLElements=False)
page = parser.parse(f)

for elt in CSSSelector('img[src]')(page):
    href = urlparse.urljoin(f.geturl(), elt.attrib['src'])
    print 'downloading ' + href
    localfile = open('dump/'+href.split('/')[-1], "wb")
    localfile.write(remotefile.read())
    localfile.close()

Get the URL of all the links in a page and jump to a random page

import random
import urllib2, urlparse, html5lib, lxml
from lxml.cssselect import CSSSelector

targets = ['http://www.volkskrant.nl/']

while True:
    target = random.choice(targets)
    print '*** '+target+' ***'
    request = urllib2.Request(target)
    request.add_header("User-Agent", "Mozilla/5.0 (X11; U; Linux x86_64; fr; rv:1.9.1.5) Gecko/20091109 Ubuntu/9.10 (karmic) Firefox/3.5.5")
    f=urllib2.urlopen(request)

    parser = html5lib.HTMLParser(tree=html5lib.treebuilders.getTreeBuilder("lxml"), namespaceHTMLElements=False)
    page = parser.parse(f)

    targets = []

    for links in CSSSelector('a[href]')(page):
        href = urlparse.urljoin(f.geturl(), links.attrib['href'])
        if href.split(':')[0] == 'http':
            targets.append(href)

Get the URL of all the links in a page and jump to a random page AND BE SMART

import random
import urllib2, urlparse, html5lib, lxml
from lxml.cssselect import CSSSelector

targets = ['http://www.volkskrant.nl/']

while True:
    target = random.choice(targets)
    print '*** '+target+' ***'

    # try to open URL ...
    try:
        request = urllib2.Request(target)
        request.add_header("User-Agent", "Mozilla/5.0 (X11; U; Linux x86_64; fr; rv:1.9.1.5) Gecko/20091109 Ubuntu/9.10 (karmic) Firefox/3.5.5")
        f=urllib2.urlopen(request)

        # Is it really something that I can parse? srsly?
        try:
            parser = html5lib.HTMLParser(tree=html5lib.treebuilders.getTreeBuilder("lxml"), namespaceHTMLElements=False)
            page = parser.parse(f)
        except ValueError, err:
            print "Value Error:", err, target

        links = []
        if CSSSelector('a[href]')(page): # Any links for me?
            for link in CSSSelector('a[href]')(page):
                href = urlparse.urljoin(f.geturl(), link.attrib['href'])
                if href.split(':')[0] == 'http': # No js links
                    links.append(href)
        if links: # Anything left?
            targets = links


    # ... catch HTTP and URL errors
    except urllib2.HTTPError, err:
        print "HTTP Error:",err.code , target
        print "trying other URL"
    except urllib2.URLError, err:
        print "URL Error:",err.reason , target
        print "trying other URL"