文本文件编辑和行写

Question

I have a slight problem with my code.

First the code:

import os
import subprocess
import httplib, urllib

for ip in range(1,255):

   ip_addr = "192.168.1." + str(ip)
   res = subprocess.call(["ping", ip_addr, "-c1", "-W1", "-q"], stdout=open(os.devnull,'w'))
   if res == 0:
      print (ip_addr) + " reachable"
   else:
      print (ip_addr) + " not reachable"

   f = open('state_All.txt','r')
   prestate = f.readline(ip)
   f.close()
   prestate = ord(prestate)
   res = res + 97
   if not prestate == res:
      if prestate == 97:
         conn = httplib.HTTPSConnection("api.pushover.net:443")
         ## The Code in here which I have deleted out is definitely not the problem,
         ## works 100% safe and can't be share beacuse of security problems.
          }), { "Content-type": "application/x-www-form-urlencoded" })
         conn.getresponse()
      else:
         conn = httplib.HTTPSConnection("api.pushover.net:443")
         ## The Code in here which I have deleted out is definitely not the problem,
         ## works 100% safe and can't be share beacuse of security problems.
          }), { "Content-type": "application/x-www-form-urlencoded" })
         conn.getresponse()
   f = open('state_All.txt','w')
   res = str(unichr(res))
   data = (res[ip])
   f.writelines(data)
   f.close()

Problem:

Reading some specific lines in the .txt works but I can't write on a specific line the measured state afterwards,

I got this error:

Traceback (most recent call last):
  File "ping_All.py", line 48, in <module>
    data = (res[ip])
IndexError: string index out of range

Hope someone can help me with it.

Answer 1

When you try access an item from that string, you get index out of range . This means that you tried to access an item, in your case a Character, where the index ( ip ) was either larger than the length of res or smaller than 0.