Ok, long story: I'm trying to solve level 4 of the Python Challenge. I hate to post here, but the hint forum over there is dead. Here's the link: http://www.pythonchallenge.com/pc/def/linkedlist.php
Apparently you need to use a linked list to solve it, so I read up on them but I still don't understand how to implement one to solve this problem. (Any hints there would be appreciated too.) So I wrote this code instead. It goes to each URL, reads the source code, gets the next number, etc. I realize it uses some terrible tricks, like the regex and the try/except clause, which is way too specific to solve the problem in a general way. Anyway, here's the code: # Python Challenge, level 4 import urllib import re url = 'http://www.pythonchallenge.com/pc/def/linkedlist.php?nothing=' pattern = re.compile(r'\bnext nothing is (\d+)') def getNextNum(url): global pattern global nextNum site = urllib.urlopen(url) try: source = site.read() site.close() number = re.search(pattern, source).group(1) except: print nextNum number = str(int(nextNum) / 2) return number nextNum = '12345' f = open(r'C:\Python24\myscripts\challenges\numbers.txt', 'w') try: for x in range(300): f.write(nextNum + '\n') nextNum = getNextNum(url + nextNum) finally: f.close() print url + nextNum Now, I tried this earlier on my work computer and it got as far as printing out two 'nextNum's in the except block, then it appeared that the website timed out and I could no longer access it for a while. I tried later on my home computer and now I keep getting this error: Traceback (most recent call last): File "C:\Python24\myscripts\challenges\linked_list.py", line 27, in -toplevel- nextNum = getNextNum(url + nextNum) File "C:\Python24\myscripts\challenges\linked_list.py", line 12, in getNextNum site = urllib.urlopen(url) File "C:\Python24\lib\urllib.py", line 82, in urlopen return opener.open(url) File "C:\Python24\lib\urllib.py", line 190, in open return getattr(self, name)(url) File "C:\Python24\lib\urllib.py", line 322, in open_http return self.http_error(url, fp, errcode, errmsg, headers) File "C:\Python24\lib\urllib.py", line 339, in http_error return self.http_error_default(url, fp, errcode, errmsg, headers) File "C:\Python24\lib\urllib.py", line 579, in http_error_default return addinfourl(fp, headers, "http:" + url) File "C:\Python24\lib\urllib.py", line 871, in __init__ addbase.__init__(self, fp) File "C:\Python24\lib\urllib.py", line 818, in __init__ self.read = self.fp.read AttributeError: 'NoneType' object has no attribute 'read' I didn't get this before, so I wonder if it's a website error. There seems to be a problem with getting the source code. It also appears that the script, when run at home, doesn't get as far as the same script when I ran it earlier today at work. So I figure it's either a website problem, or some kind of strange difference between the two computers I'm using (but both use 2.4.3 and nothing else seems different). I hope someone can point me in the right direction. I'm curious why it fails in a different way at home than at work, but also I'd like to know if it's even possible to solve the problem in this way, or if I *have* to use a linked list. -- http://mail.python.org/mailman/listinfo/python-list
