Python code getting stuck while trying to handle an exception

Question

Code:

def ScanNetwork():
        nmScan = nmap.PortScanner()
        s = nmScan.scan("192.168.1.1/24", '0-4444', arguments="-O")
            
        for host in nmScan.all_hosts():
            if nmScan[host].state() == "up":
                print("Host : %s (%s)" % (host, nmScan[host].hostname()))
                try:
                    print("Version: " + s['scan'][host]['osmatch'][0]['name'] + "\nType: " + s['scan'][host]['osmatch'][0]['osclass'][0]['type'])
                except:
                    print("An Error occured while scanning this host!\nNo extra info was collected!")
                    continue
                for proto in nmScan[host].all_protocols():
                    print("---------------------------")
                    print("\nProtocol : %s" % proto)
                    lport = nmScan[host][proto].keys()
                    lport = sorted(lport)
                    for port in lport:
                        print("\nport: " + f'{port}' + "\tstate: " + nmScan[host][proto][port]['state'])
                print("---------------------------\n")  
        print("\n\nScan Completed!")
ScanNetwork()

Sometimes an exception occurs when the nmap fails to identify the Version or the Os running in a host. (It's a KeyError exception)

The part which is supposed to handle that exception is this:

try:
   print("Version: " + s['scan'][host]['osmatch'][0]['name'] + "\nType: " + s['scan'][host]['osmatch'][0]['osclass'][0]['type'])
except:
    print("An Error occured while scanning this host!\nNo extra info was collected!")
    continue

I of course assume that there's nothing wrong with nmap's output and I've again made a huge beginner mistake and that's the reason my code is getting stuck..

Notes:

• I've left the script running over night incase it returned some useful info but nothing happened!
• Please do not tell me that I need to quit using the nmap module and turn to nmap3

Having tired you with all the above, does anyone know a way to still handle that exception without the code getting stuck?

Answer 1

You have forgotten to add the type of the exception to excpect while running the code inside the try-except block.

This should fix it:

try:
   print("Version: " + s['scan'][host]['osmatch'][0]['name'] + "\n" + "Type: " + s['scan'][host]['osmatch'][0]['osclass'][0]['type'])
except KeyError:
    print("An Error occured while scanning this host!\nNo extra info was collected!")
    continue

In case you want to catch any possible exception that could occur (and yes custom ones included) then you should use the following code:

try:
   <some critical code with possible exceptions to catch>
except Exception:
   print("An exception occured")