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

You should not catch *all* exceptions. Catch specific exceptions only instead. — Martijn Pieters, Jun 13 '13 at 17:12
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. — 2rs2ts, Jun 13 '13 at 17:14

score 1 · Answer 1 · answered Jun 13 '13 at 17:17

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

score 1 · Accepted Answer · edited May 23 '17 at 10:32

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.

score 0 · Answer 3 · answered Jun 13 '13 at 17:45

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)

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

3 Answers3