Python Try and Except - The script get hung on the except

Question

I have a small script that will check to see if a list of devices are either ssh or telnet enable. Here is my code:

import socket
import sys
file = open('list', 'r')
file = file.readlines()
list = []
for i in file:
 i=i.replace('\n','')
 list.append(i)
for i in list:
 s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
 try:
 s.connect((i, 22))
 s.shutdown(2)
 s.close()
 print (i+' SSH ')
 except:
 try:
 s.connect((i, 23))
 s.shutdown(2)
 s.close()
 print (i+' Telnet')
 except:
 print (i + 'disable')
 pass

When I get an exception, I have to hit ctrl + c to go to the next device. What are am I doing wrong? Thanks

• Martijn Pieters: You should not catch all exceptions. Catch specific exceptions only instead.
• 2rs2ts: Try except Exception as e and then figure out the type of e by printing type(e). Also try printing before each statement in your try block so you know where you're getting stuck.
• dansalmo: You should not use list as a name since it a built in name.
• Aya: One word: nmap

Answer 1

did you try adding a timeout?

import socket
import sys
with open('list', 'r') as f:# file is a global class
 # per default it reads the file line by line, 
 # readlines() loads the whole file in memory at once, using more memory
 # and you don't need the list.
 for i in f:
 i=i.replace('\n','')
 s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
 s.settimeout(10)
 try:
 s.connect((i, 22))
 s.shutdown(2)
 s.close()
 print (i+' SSH ')
 except:
 try:
 s.connect((i, 23))
 s.shutdown(2)
 s.close()
 print (i+' Telnet')
 except:
 print (i + 'disable')
 pass

setting up a time out closes the stream after a timeout, otherwise it blocks forever.

Answer 2

I cannot really run the code because I don't have the list file you open on my machine. Still made few edits, any difference?

import socket
import sys
file = open('list', 'r')
file = file.readlines()
list = []
for i in file:
 i=i.replace('\n','')
 list.append(i)
for i in list:
 s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
 try:
 s.connect((i, 22))
 s.shutdown(2)
 s.close()
 print (i+' SSH ')
 except:
 s.connect((i, 23))
 s.shutdown(2)
 s.close()
 print (i+' Telnet')
 else:
 print (i + 'disable')
 pass

Answer 3

Again I can't really run the code because of lack of the file 'list' (rather misleading..) but I've done some further refactoring and offered up a suggestion.

import socket
import sys
with open('list', 'r') as f:
 # Don't call anything 'list' as it is the name for pythons inbuilt type
 # Using `with` will automatically close the file after you've used it.
 content = f.readlines()
 # We can use a list comprehension to quickly strip any newline characters.
 content = [x.replace('\n','') for x in content]
for x in content:
 s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
 try:
 s.connect((x, 22))
 s.shutdown(2)
 s.close()
 print (x+' SSH')
 except:
 # This should catch a specific exception, e.g. TimeoutError etc
 # e.g. `except ConnectionError`
 try:
 s.connect((i, 23))
 s.shutdown(2)
 s.close()
 print (i+' Telnet')
 except:
 print (i + 'disable')
 pass

My guess is that the connection is hanging rather than hitting the exception. Maybe due to timeouts as it cannot connect.

Add a timeout option with:

s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.settimeout(60)