Token generator (does not differentiate EOF from duplicate) Takes around 2 seconds for 25k entries

tokengenerator.py

import binascii
import os
import sys
import time

start_time = time.time()

iterations = 25000
current = 0
characters = 3

f = open('numbers.txt', 'w')

while current < iterations:
    token = binascii.hexlify(os.urandom(characters)).upper()
    line = token + '\n'
    f.write(line)
    current += 1
    print token
f.close()

f = open('numbers.txt', 'r')
print "Check if it is duplicated..."
duplicate = 1
while duplicate:
    for i in f.readlines():
        if line == i:
            print "KILL IT WITH FIRE! (wait, is this EOF??)"
            token = binascii.hexlify(os.urandom(6))
            line = token + '\n'
        else:
            sys.stdout.write(".")
            #sys.stdout.write('\r' + ' ' * (characters / 2))
    duplicate = 0
elapsed_time = time.time() - start_time

print "Generation took: %s" % time.strftime('%H:%M:%S', time.localtime(elapsed_time))