telnet（telnetlib）超时后如何让Python代码继续

Question

I am using Python for Automated telnet program using telnetlib. The problem is: when the device that I am trying to telnet to doesn't responsd, means timeout; the program gives me timeout message and doesn't continue to next commands.

My Code:

import telnetlib  
HOST = ("x.x.x.x")  
USER = ("xxxxx")  
PWD = ("yyyyy")  
ENABLE = ("zzzzz")  
TNT = telnetlib.Telnet(HOST, 23, 5)                    
TNT.read_until(b"Username:")  
TNT.write(USER.encode('ascii') + b"\n")  
TNT.read_until(b"Password:")  
TNT.write(PWD.encode('ascii') + b"\n")  
TNT.write(b"enable\n")  
TNT.read_until(b"Password:")  
TNT.write(ENABLE.encode('ascii') + b"\n")  
TNT.write(b"terminal length 0\n")  
TNT.write(b"show run\n")  
TNT.write(b"exit\n")  
print (TNT.read_all().decode('ascii'))  
TNT.close()  
raw_input ("Press any Key to Quit: ")  

Error Message:

Traceback (most recent call last):  
  File "D:\Python\Telnet (Python 2.7) V1.5.py", line 8, in <module>  
    TNT = telnetlib.Telnet(HOST, 23, 5)  
  File "C:\Python27\lib\telnetlib.py", line 209, in __init__  
    self.open(host, port, timeout)  
  File "C:\Python27\lib\telnetlib.py", line 225, in open  
    self.sock = socket.create_connection((host, port), timeout)  
  File "C:\Python27\lib\socket.py", line 571, in create_connection  
    raise err  
timeout: timed out  
>>> 

How can let the program to just notify me that this device isn't reachable and let it continue with the next commands ??

Answer 1

将操作包装在try块中，并在catch块中处理异常。

Answer 2

Python terminates your program whenever as exception arrives. For handling exception you need to wrap it in try, catch statements.

Put your telnet statement in try statement and catch exception using except as shown below:

import telnetlib  
HOST = ("x.x.x.x")  
USER = ("xxxxx")  
PWD = ("yyyyy")  
ENABLE = ("zzzzz")  
try:
    TNT = telnetlib.Telnet(HOST, 23, 5)                    
except:
    print "<your custom message>"
    pass
TNT.read_until(b"Username:")  
TNT.write(USER.encode('ascii') + b"\n")  
TNT.read_until(b"Password:")  
TNT.write(PWD.encode('ascii') + b"\n")  
TNT.write(b"enable\n")  
TNT.read_until(b"Password:")  
TNT.write(ENABLE.encode('ascii') + b"\n")  
TNT.write(b"terminal length 0\n")  
TNT.write(b"show run\n")  
TNT.write(b"exit\n")  
print (TNT.read_all().decode('ascii'))  
TNT.close()  
raw_input ("Press any Key to Quit: ")  

Answer 3

The exception you're looking for is socket.timeout . so:

import socket
try:
    TNT = telnetlib.Telnet(HOST, 23, 5)
except socket.timeout:
    sulk()

Which I discovered in this way:

>>> try:
...   t = telnetlib.Telnet("google.com", 23, 5)
... except:
...   import sys
...   exc_info = sys.exc_info()
>>> exc_info
(<class 'socket.timeout'>, timeout('timed out',), <traceback object at 0xb768bf7c>)

It might be that timeout is too specific. You might instead prefer to catch any IOError

try:
    TNT = telnetlib.Telnet(HOST, 23, 5)
except IOError:
    sulk()