Can't escape while loop

Question

I am a beginning programmer writing in Python 3.5 for my Computer Concepts III class. This week we are working on data validation using try/except blocks and Boolean flags, modifying a program we made last week. I've almost completed my weekly assignment except for one thing. I can't figure out why I'm getting stuck in a while loop. This is the loop in question:

while not valid_data:
    cont = input("Would you like to order another? (y/n) ")
    if cont.lower not in yorn:
        valid_data = False
    else:
        valid_data = True

yorn is ["y", "n"]

Here is the whole program for context:

# Program       Lesson 6 Order
# Programmer    Wiley J
# Date          2016.02.13
# Purpose       The purpose of this program is to take an order for cookies.


# Import Class/Format Currency
import locale
locale.setlocale(locale.LC_ALL, '')

# Define Variables
boxes = 0
cost = 3.50
qty = 0
items = 0
yorn = ["y", "n"]

# Banner
print("Welcome to The Cookie Portal")

# Input
valid_data = False

while not valid_data:
    name = input("Please enter your name: ")
    if len(name) > 20:
        print()
        print("Not a valid name")
        valid_data = False
    elif len(name) == 0:
        print("You need to enter a name")
        valid_data = False
    else:
        print("Hello", name)
        valid_data = True

cont = input("Would you like to place an order? (y/n) ")

# Process
while cont.lower() not in yorn:
    cont = input("Would you like to place an order? (y/n) ")

while cont.lower() == "y":

    valid_data = False

    while not valid_data:
        print("Please choose a flavor:")
        print("1. Savannahs")
        print("2. Thin Mints")
        print("3. Tagalongs")
        try:
            flavor = int(input("> "))
            if flavor in range (1, 4):
                items += 1
                valid_data = True
            else:
                valid_data = False
        except Exception as detail:
            print("Error", detail)

    valid_data = False

    while not valid_data:
        try:
            boxes = int(input("How many boxes? (1-10) "))
            if boxes not in range (1, 11):
                print("Please choose a number between 1 and 10")
                valid_data = False
            else:
                qty += boxes
                valid_data = True
        except Exception as detail:
            print("Error", detail)
            print()
            print("Please enter a number")

    valid_data = False

    while not valid_data:
        cont = input("Would you like to order another? (y/n) ")
        if cont.lower not in yorn:
            valid_data = False
        else:
            valid_data = True



# Output
if cont.lower() == "n":
    cost *= qty      
    print()
    print("Order for", name)
    print("-------------------")
    print("Total Items = {}".format(items))
    print("Total Boxes = {}".format(qty))
    print("Total Cost = {}".format(locale.currency(cost)))
    print()
    print("Thank you for your order.")

I wouldn't be surprised if there are other issues with this code but they are most likely by design as per the requirements of the assignment. Any additional feedback is welcome.

Answer 1

It seems you are missing function-paranthesis in the end of "lower", like so:

if cont.lower() not in yorn:

Answer 2

Your problem is here:

if cont.lower not in yorn:

lower is a method, it should be:

if cont.lower() not in yorn: