Pedagogical reasoning behind a minor difference in two loops
This is a really good place to introduce boolean variables (or just to use them, if they've already been introduced. It also introduces the idea of descriptive variable names.  

user_wishes_to_continue = True

while user_wishes_to_continue:
    answer = raw_input("Do you wish to continue?")
    if answer != "yes":
        user_wishes_to_continue = False

print ("Good bye")


Note: here I use raw_input, which returns the user input as a string, rather than input, which interprets the  user input as python code (meaning that you have to put "yes" with the quotation marks each time.