A simple script that asks a user to guess the number. It uses a while loop that will continue to ask for user input until the condition is met. We then use exit() to break the loop.

from sys import exit

while True:
    print "Try and guess the number."
    guess = raw_input("> ")

    if guess == "7":
            print "You guessed correctly."
            exit(0)

    else:
        print "Wrong."