Supermarket Self-Service Checkout: Python

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Question :

ITECH1400 - Assignment 1 – Supermarket Self-Service Checkout

Assignment Overview 

You are tasked with creating a text-based program for simulating a supermarket self-service checkout using the Python 3 programming language. The assignment is broken up into four main components: 1.) Design and model two classes: Product and Checkout Register, 2.) Create an activity chart which describes the behaviour of the checkout system, 3.) Create a computer program that allows a user to interactively check out a number of products, then provides an opportunity to enter some virtual money to pay for the products and finally and prints out a receipt for the user (to the screen, not on paper), and finally 4.) Explain and integrate some code into your checkout program that places the products purchased into virtual shopping bags. Your submission should consist of one Microsoft Word or LibreOffice document containing the first two parts of the assignment, and three Python scripts that implement the computer program (, and The script runs the main logic of the program and will use instances of the CheckoutRegister and Product classes to simulate checking out of the supermarket. You are provided with a Microsoft Word template to help you complete the first two parts of this assignment. Towards the end of this document you will also be provided with the output of a simulated run of the completed computer program which may help you with this assignment.

Assignment Part 1 Details

Class Design Think of a product that you can buy from a supermarket, like maybe a can of soup or an apple. Start by listing all the properties of that object that you can think of – try to come up with at least ten general properties of a Product and write these down in your Assignment_Part_1_ Microsoft Word document. Next, use the process of abstraction to cut the number of properties back to only four ‘key’ properties – write these down in the next section of your Word document. Take a look at the week 2 lecture slides if you need a reminder on how to go about this. Now, fill in the class diagram for your Product class in the Word document template provided. Your product class does not have to have any methods (i.e. functions) associated with it to perform any actions other than a constructor which takes and set the four key properties that you’ve identified. Next we’ll move on to CheckoutRegister class – think about what information the checkout has to keep track of to allow you to successfully check out of the supermarket. There will only really be three key properties that the CheckoutRegister cares about, and the CheckoutRegister class should have the following four methods available: 1) A default constructor that takes no arguments and initialises a new object and its properties, 2) accept_payment(some_amount), 3) scan_item(some_product), and 4) print_receipt(). Fill in the class diagram for the CheckoutRegister class in the Word template, and that’s the first part completed!

Assignment Part 2 Details

Activity Flowchart Using either the online website (preferred), or the applications Visio or Powerpoint – create an activity diagram of how the program should operate to successfully scan one or more products, accept payment, provide change and print a receipt for the user. Make sure to use the correct symbols in your diagram for starting, processes, decisions/branches, and ending the process. Although you should be familiar with how a self-checkout works, if not then you can always go to a local supermarket with a self-checkout and buy a packet of chewing gum or something – or take a look at a YouTube video of self-service checkout, such as this one: Don’t worry about loyalty/rewards cards to taking payment through debit or credit cards, our CheckoutRegister will only accept cash – although you can enter multiple denominations via multiple calls to the accept_money(some_amount) method. For example, calling accept_money(5.0) and then accept_money(2.0) will mean that the CheckoutRegister knows that you have entered a total of $7.00. Also note that you can start the entire checkout process off by simply scanning a product. Once you have completed your activity flowchart, add it to your assignment template document.

Assignment Part 3 Details

Software Implementation You are free to implement the software however you see fit, however the functionality of the software should be able to match the following output. Note that in the below run of the program I have ‘hard-coded’ a small number of Product instances so that products exist which can they can be checked out – in your code you should do the same. Your program does not have to have the facility to add new products – just define a few and use them as demonstrated below. If the final option of (N)ext customer is chosen, the program should run again.

Part 4 – Code Explanation and Use You are provided with the following two functions which you should 1. Analyse to determine what they do & provide documentation comments for, and 2. Incorporate into your final program solution. Wherever there is a # followed by some underscores in the code below, you should write a short comment explaining what the below section of code is doing, and if there is space why it is doing it. Do part 1 of the above in the provided assignment 1 template document, rather than here! # Function to: ___________________________ def get_float(prompt):  # ____________________________________  value = float(0.0)  # ____________________________________  while True:  try:  # ____________________________________  value = float(input(prompt))  # ____________________________________  if value < 0.0:  print("We don't accept negative money!")  continue  # ____________________________________  break  # ____________________________________  except ValueError:  print('Please enter a valid floating point value.')  # ____________________________________  return value # Function to: ___________________________ def bag_products(product_list):  # ____________________________________  bag_list = []  non_bagged_items = []  MAX_BAG_WEIGHT = 5.0  # ____________________________________  for product in product_list: # ____________________________________  if product.weight > MAX_BAG_WEIGHT:  product_list.remove(product)  non_bagged_items.append(product)  # ____________________________________  current_bag_contents = []  current_bag_weight = 0.0  # ____________________________________  while len(product_list) > 0:  # ____________________________________  temp_product = product_list[0]  product_list.remove(temp_product)  # ____________________________________  if current_bag_weight + temp_product.weight <= MAX_BAG_WEIGHT:  # ____________________________________  current_bag_contents.append(temp_product)  current_bag_weight += temp_product.weight  # ____________________________________  else:  bag_list.append(current_bag_contents)  # ____________________________________  current_bag_contents = [temp_product]  current_bag_weight = temp_product.weight  # ____________________________________  if (len(product_list) == 0):  bag_list.append(current_bag_contents)  # ____________________________________  for index, bag in enumerate(bag_list):  output = 'Bag ' + str(index + 1) + ' contains: '  # ____________________________________  for product in bag:  output += + '\t'  print(output, '\n')  # ____________________________________  if (len(non_bagged_items) > 0):  output = 'Non-bagged items: '  # ____________________________________  for item in non_bagged_items:  output += + '\t'  print(output,'\n') ITECH1400 – Foundations of Programming – SE

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Answer :


Assignment Part 1 Details – Class Design

Product Details / Attributes/Properties

  1. Product Id
  2. Product Name
  3. Product Price
  4. Weight
  5. Mfg.  

Selected Product Properties through data abstraction

  1. Product Id
  2. Product Name
  3. Price
  4. Weight

Checkout Register Details / Attributes/Properties

  1. Total Sale
  2. Welcome Message
  3. Type
  4. Product Inventory
  5. Cash Reader

Assignment Part 2 Details – Activity Flowchart

activity flowchart

Assignment Part 3 Details – Software Implementation

Part 4 – Code Explanation and Use

# Function to: get a float value and return it to calling function

def get_float(prompt):

# float variable to read value , initial value is set to 0.0

value = float(0.0)

# loop to continue till valid value is entered

while True:


# get a string from user and cast it to float

value = float(input(prompt))

# value eneterd is less then 0

if value < 0.0:

print("We don't accept negative money!")


# this value is a valid value greater then 0


# the value eneterd was not a valid float value

except ValueError:

print('Please enter a valid floating point value.')

#return the valid value eneterd by the user

return value

#Function to: pack the purchased items into bag

def bag_products(product_list):

# take empty list of bags and set max Bag weight to 5

bag_list = []

non_bagged_items = []


# for each product in the list f products carry the below functionality

for product in product_list:

# this product has more weight then the max allowed weight

# i.e. this product cannot be packed into any bag

if product.Weight > MAX_BAG_WEIGHT:



# take a new empty bag and set its weight to 0

current_bag_contents = []

current_bag_weight = 0.0

# loop will continue till there is even a single item in the products list

while len(product_list) > 0:

# take temp_product as the first item in the product's list

temp_product = product_list[0]


# this bag weight + weight of the current product is less then or equal to

# what the bag can carry i.e. this product can be added to current bag

if current_bag_weight + temp_product.Weight <= MAX_BAG_WEIGHT:

# pack this product into the current bag


current_bag_weight += temp_product.Weight

# add this bag to the list of bags



# take a new bag and add the current product to this bag

# also set the current weight of the bag equal to the the weight of this product

current_bag_contents = [temp_product]

current_bag_weight = temp_product.Weight

# there are no remaining items, all were packed, add current bag to the list of bags

if (len(product_list) == 0):


# go through each bag in the list of purchased products 

for index, bag in enumerate(bag_list):

output = 'Bag ' + str(index + 1) + ' contains: '

# print the contents of each bag

for product in bag:

output += product.productName + '\t'

print(output, '\n')

# there are some items which were not packed

if (len(non_bagged_items) > 0):

output = 'Non-bagged items: '

# go through each abg in the list of purchased products 

for item in non_bagged_items:

output += item.productName + '\t'