I thought I would write my first python function for this one.  They appear to need to be at the top of the script though with a little casual searching I couldn’t confirm that.

Python 2.7.2 Solution

This got me there but is pretty flaky and needed manually fixing to get to the answer.

import urllib, re
count = 1

def getNextCode(lastCode):
    while True:
        try:
            page = urllib.urlopen('http://www.pythonchallenge.com/pc/def/linkedlist.php?nothing=%s' % lastCode).read()
            code = re.findall('(?<=and the next nothing is )\w*',page)
            print "Code %i is %s.  \nPage message was '%s'.\nPage tried was http://www.pythonchallenge.com/pc/def/linkedlist.php?nothing=%s'.\n" % (count, code[0], page, lastCode)
            return code
        except (IndexError, NameError):
            print "Error: Page message was '%s'\nPage was: http://www.pythonchallenge.com/pc/def/linkedlist.php?nothing=%s'." % (page,lastCode)
            return False
        
nextCode = getNextCode('12345')

count = 1

for count in range (1,400):
        if count == 84:
            nextCode[0] = int(nextCode[0])/2 
        nextCode = getNextCode(nextCode[0])

Python 3.2.3 Solution

This deals with the message that you must divide by two when you get 16044 as a code. It also loads the page.  The 3.2.3 has a very different urllib approach.  3.2.3 seems to do crazy stuff with variable types.

import urllib.request, re, webbrowser
count = 1
        
def getNextCode(lastCode):
    while True:
        try:
            if lastCode == '16044': lastCode = str(16044 / 2)
            page = urllib.request.urlopen('http://www.pythonchallenge.com/pc/def/linkedlist.php?nothing=%s' % lastCode).read()         
            code = re.findall(r'(?<=and the next nothing is )\w*',page.decode("utf-8"))
            print ("\nCode %i is %s.\nPage tried was http://www.pythonchallenge.com/pc/def/linkedlist.php?nothing=%s'.\nPage message was '%s'." % (count, code[0], lastCode, page.decode("utf-8")))
            return code
        except (IndexError, NameError):
            print ("Error: Page message was '%s'\nPage was: http://www.pythonchallenge.com/pc/def/linkedlist.php?nothing=%s'." % (page,lastCode))
            return False
      
nextCode = getNextCode('12345')

count = 1

for count in range (1,400):
    if nextCode != False:
        answer = nextCode[0]
        nextCode = getNextCode(nextCode[0])
    else:
        new = 2 # open in a new tab, if possible
        test4url = "http://www.pythonchallenge.com/pc/def/" + urllib.request.urlopen('http://www.pythonchallenge.com/pc/def/linkedlist.php?nothing=%s' % answer).read().decode("utf-8")
        webbrowser.open(test4url,new=new)  
        break
print ("Done.")