Python For Loop Only Looping Once (for each line in text file)

Question

I'm currently on my third year of a Software Development degree at I'm thinking about branching out into some security modules next year, I picked up "Violent Python" as an intro and to learn a new language, however I'm stuck on the first exercise.

I'm no newbie to programming and perhaps I'm just tired - it's been a long day on little sleep - but this simple script wont work:

import crypt
def testPass(cryptPass):
salt = cryptPass[0:2]
 dictFile = open('dictionary.txt')
 for word in dictFile.readlines():
  word = word.strip('\n')
  print "[*] Attempting password: "+word+"\n"
  cryptWord = crypt.crypt(word,salt)
  if (cryptWord == cryptPass):
   print "[+] Found Password: "+word+"\n"
   return
  print "[-] Password Not Found.\n"
  return
def main():
 passFile = open('passwords.txt')
 for line in passFile.readlines():
  if ":" in line:
   user = line.split(':')[0]
   cryptPass = line.split(':')[1].strip(' ')
   print "[*] Cracking Password For: "+user
   testPass(cryptPass)
if __name__ == "__main__":
 main()

Passwords.txt has two users from /etc/passwd (victim and root) and it loops through them fine. I have three passwords in my dictionary.txt and for some reason it only attempts the first password:

[*] Cracking Password For: victim
[*] Attempting password: break 

[-] Password Not Found.

[*] Cracking Password For: root
[*] Attempting password: break 

[-] Password Not Found.

Can someone explain why the code above lifted from the book didn't work? I managed to solve the problem by using a 'with open' instead:

with open('dictionary.txt') as f:
 for word in f:
  word = word.strip("\n")
  cryptWord = crypt.crypt(word,salt)
  if (cryptWord == cryptPass):
   print "[+] Found Password: "+word+"\n"
   return
  print "[-] Password Not Found.\n"
  return

Please review your code indentation (ideally 4 spaces per level) - whitespace is important in Python! — jonrsharpe
– jonrsharpe, Commented Jan 6, 2014 at 22:40

moustachio · Accepted Answer · 2014-01-06 22:50:47Z

This is an indentation mistake. For things to work properly, your 'testPass' function should look like this:

def testPass(cryptPass):
    salt = cryptPass[0:2]
    dictFile = open('dictionary.txt')
    for word in dictFile.readlines():
        word = word.strip('\n')
        print "[*] Attempting password: "+word+"\n"
        cryptWord = crypt.crypt(word,salt)
        if (cryptWord == cryptPass):
            print "[+] Found Password: "+word+"\n"
            return
     print "[-] Password Not Found.\n"
     return

That way, it will loop through every word in the dictionary, and return once a password is found. If it loops through everything without finding it, it should then print "password not found". Your problem is that your code (spaced out a bit for clarity) is actually indented like this:

def testPass(cryptPass):
    salt = cryptPass[0:2]
    dictFile = open('dictionary.txt')
    for word in dictFile.readlines():
        word = word.strip('\n')
        print "[*] Attempting password: "+word+"\n"
        cryptWord = crypt.crypt(word,salt)
        if (cryptWord == cryptPass):
            print "[+] Found Password: "+word+"\n"
            return
        print "[-] Password Not Found.\n"
        return

See the difference? Like this, it will only check the first word, since the second "return" is within the loop. Please verify your indentation (ideally 4 spaces, as @jonrsharpe said, or a tab) and try it again. I suspect this will solve your problem.

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