Python Question: A system for ordering pizza

A dialog system (or conversational agent) is a computer program intended to communicate with humans in natural language, following a specific dialog structure to accomplish a specific tasks. Common examples are automatic phone systems for flight reservations or personal assistants such as Siri and Alexa. In this problem we will use functions to write a very basic dialog system (with limited vocabulary). The system should allow the user to order from an Italian restaurant by asking specific questions. Here is an example Dialog:

Python prints: "Hello, would you like pizza or salad?" User types: "pizza" Python: "Small, medium, or large?" User: "large" Python: "Add a topping: pepperoni, mushrooms, spinach, or say 'done'" User: "mushrooms" Python: "Add a topping: pepperoni, mushrooms, spinach, or say 'done'" User: "spinach" Python: "Add a topping: pepperoni, mushrooms, spinach, or say 'done'" User: "done" Python: "You ordered a large pizza with mushrooms and spinach. Place another order or say 'done'. Hello, would you like pizza or salad?" User: "salad" Python: "Would you like a garden salad or greek salad" User: "greek" Python: "please choose a dressing: vinaigrette, ranch, blue cheese, lemon" User: "blue cheese" Python: "You ordered a large pizza with mushrooms and spinach and a greek salad with blue cheese dressing. Place another order or say done'. Hello, would you like pizza or salad?" User: "done" Python: "Your order has been placed. Goodbye."

Implement functions to prompt the user, as illustrated in the diagram below. For example, the salad() function should ask the user for a type of salad. Then the salad() functions calls the dressing() method to asks for a dressing.

All functions return a string, so that you can assemble the order as a string in the calling function. The dressing() function would return the type of dressing, for example "blue cheese". The salad() function would combine the dressing and the salad type into "greek salad with lemon dressing". Finally, the select_meal() function would assemble the complete order in a string.

The following diagram illustrates the order in which the functions should be called and how the result string should be assembled from the return values incrementally.

Some complications:

The toppings() function should ask for toppings repeatedly until the user types "done". The return value of the toppings method should be a single string including the toppings, for example "pepperoni and mushrooms and spinach".

The select_meal function should ask the user repeatedly to add an item until the user types "done". It should assemble a string representing the complete order.

Hints:

- None of the functions take any parameters. The important part in this problem is that you are calling functions from within other functions ("nested" function calls).

- Use string formatting with {} place holders to assemble the strings. Make sure to write all functions specified in the diagram, and only those functions with the specified behavior.

a Targe pizza with mushrooms and spinach and a greek salad with blue cheese dressing select meal) Hello, would you like pizza or salad? (ask repeatedly) a large pizza with mushrooms and spinach a greek salad with blue cheese dressing pizza() small medium or large? salad() Would you like a garden salad or greek salad? mushrooms and spinach blue cheese toppings() Add a topping... dressing() Please choose a dressing... (ask repeatedly)