'112.12.12.21', 'Sid'
'100.12.123.1','ABC'

header = "IP" " Name"
file = open(r'C:UsersDesktoptestfile.txt','w')

file.write(header+ 'n')
file.write('123 ABC'+ 'n')
file.write('345 DEF')

file.close()
file ["IP"] = file["IP"].replace(regex="((?<=[0-9])[0-9]|(?<=.)[0-9])",value="X")
print (file.read)