making a login function for python code example

Example: python code for login page

CorrectUsername = surname[0:3] + firstname[0:3]

loop = 'true'
while (loop == 'true'):
    username = input("Please enter your username: ")
    if (username == CorrectUsername):
    	password = input("Please enter your password: ")
        if (password == CorrectPassword):
            print("Logged in successfully as ") + username
            loop = 'false'
        else:
            print "Password incorrect!"
    else:
        print "Username incorrect!"