[Tutor] close failed in file object destructor:

[Navneet]

Hi,

I am trying to search a list for prime numbers but it's throwing me an 
error at line no.25.
I am not able to figure what exactly is the prob
ne help ??? Error is this:
$ python "prime1 - Copy.py"
Unhandled exception in thread started by
Traceback (most recent call last):
   File "prime1 - Copy.py", line 25, in findPrime
close failed in file object destructor:
Error in sys.excepthook:

program is below: Numberlist is number range from 1..1000


import sys
import threading
import thread
import time

class FindPno():

     c = []
     f = open("A;\Numberlist.txt")
     for i in f:
         c.append(i)
     f.close()
     ##print len(c)
     ##Thread should start here
     def __init__(self):
         thread.start_new_thread(self.findPrime,(1,))

     def findPrime(self,tid):
         global tlock
##        print "I am here"
         tlock = thread.allocate_lock()
##        print "I am here"
         tlock.acquire()
##        print "I am here"
         for i1 in range(len(c)):               ##this is the 25th line
             for i2 in range(2,int(c[i1])):

                 if int(c[i1]) == 1:
                     print "I am here"
                     tlock.release()
                     break
                 if int(c[i1]) == 2:
                     print c
                     print "I am here"
                     tlock.release()
                     break
                 rem = int(c[i1])%i2
                 if rem == 0:
                     print "I am here"
                     tlock.release()
                     break
                 if i2 == int(c[i1])-1:
                     print int(c[i1]), "This is the Thread",tid
                     print "I am here"
                     tlock.release()

         tlock.release()

if __name__ == '__main__':
     a = FindPno()

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