"yes" not defined? A little confused

Question

Returns an error on restart 'yes' is not defined . A noob to python, so not very sure what's wrong here.

restart = input("Would you like to play again? ").lower
if restart == ("yes"):
    print("Restarting.. ")
    main()
elif restart == ("no"):
    print("Bye! ")
    exit()

main()

I want for when the user types yes or no, it either exits the program or re-runs main() .

Answer 1

 restart = raw_input("Would you like to play again? ").lower()
 if restart == ("yes"):
    print("Restarting.. ")
    main()
 elif restart == ("no"):
  print("Bye! ")
  exit()

 main() 

since you are using python 2 your code should be like that