Why it doesn't go ????

[Panther]

import os
fd = os.popen('python ping.py 192.168.1.4', 'r')
if fd.readline() == 'None':
 print "I'don't ping ip"


#ip 192.168.1.4 doesn't exist
#Because it is not good !!!
#If I use it (python ping.py 192.168.1.4) it go, but if I put this in a
#script as thist it doesn't go.
#Pease help me !!!