loop = 1
users = []
def menu():
    print "Hello, and welcome to Uplink International. If you already have an\
    account, press 1 to create an account, or if you are already a user,\
    press 2 to log in. Press 0 to exit."
    print " "
    choice = input('What would you like to do? ')
    print ""
    return choice
while loop == 1:
    choice = menu()
    if choice == 0:
        print "Goodbye."
        exit
    elif choice == 1:
        print "Please enter your desired username and password (case sensitive)."
        print " "
        username = raw_input('Username: ')
        password = raw_input('Password: ')
        users.append([username, password])
        print "Account successfully created!"
        print " "
        loop = 1
    elif choice == 2:
        username = raw_input('Username: ')
        password = raw_input('Password: ')
        if [username, password] in users:
            print "DING DING DING DING DING! Access granted, you rock!"
            print " "
        else:
             print "Invalid username or password. DENIED!"
             print " "
             loop = 1