db = {}

def newuser():
    prompt = "login desired:"
    while True:
        name = raw_input(prompt)
        if db.has_key(name):
            prompt = "name taken,try again: "
            continue
        else:
            break
    pwd = raw_input("passwd:")
    db[name]= pwd 
    print "regeisted oK!\n"

def olduser():
    name = raw_input("login:")
    pwd = raw_input("passwd:")
    passwd = db.get(name)
    if passwd == pwd:
        print "welcome back," ,name
    else:
        print "login incorrect"

def showmenu():
    prompt = """
  (n) new user login
  (l) exiting user login
  (q) quit
   enter choice : """

    done = False
    while not done:
        chosen = False
        while not chosen:
            try:
                choice = raw_input(prompt).strip()[0].lower()
            except(EOFError,KeyboardInterrupt):
                choice = "q"
            print "\n you picked [%s]" % choice
            if choice not in "nlq":
                print "invalid option, try again"
            else:
                chosen = True

        if choice == "q": done = True
        if choice == "n": newuser()
        if choice == "l": olduser()

if __name__ == "__main__":
    showmenu()