09 Prove Milestone: Text Files

Purpose

Prove that you can write a Python program that reads CSV files and creates, populates, and uses a dictionary.

Problem Statement

A local grocery store subscribes to an online service that enables its customers to order groceries online. After a customer completes an order, the online service sends a CSV file that contains the customer’s requests to the grocery store. The store needs you to write a program that reads the CSV file and prints to the terminal window a receipt that lists the purchased items and shows the subtotal, the sales tax amount, and the total.

Assignment

During this milestone, you will write half of a Python program named receipt.py that prints to the terminal window a receipt for a customer’s grocery order. Specifically, by the end of this milestone, your program must contain at least these two functions:

1. main
2. read_dictionary

and must read and process these two CSV files:

• The products.csv file is a catalog of all the products that the grocery store sells.
• The request.csv file contains the items ordered by a customer.

Help

If you’re having trouble completing this assignment, reading related online documentation, using a generative AI as a tutor, or working with a human tutor will help you complete it.

Steps

Do the following:

1. Download both of these files: products.csv and request.csv and save them in the same folder where you will save your Python program.
2. Open the products.csv file in VS Code and examine it. Notice that each row in this file contains three values separated by commas: a product number, a product name, and a retail price. Also, notice that each product number in the products.csv file is unique. This means that your program can read the products.csv file into a dictionary and use the product numbers as keys in the dictionary.
3. In VS Code, create a new file and save it as receipt.py in the same folder where you saved the products.csv and request.csv files.

4. In receipt.py, write a function named read_dictionary that will open a CSV file for reading and use a csv.reader to read each row and populate a compound dictionary with the contents of the products.csv file. The read_dictionary function must have this header and documentation string:

   def read_dictionary(filename, key_column_index):
       """Read the contents of a CSV file into a compound
       dictionary and return the dictionary.
   
       Parameters
           filename: the name of the CSV file to read.
           key_column_index: the index of the column
               to use as the keys in the dictionary.
       Return: a compound dictionary that contains
           the contents of the CSV file.
       """
   

   As part of the team activity for this lesson, you already wrote a similar or the same read_dictionary function.

5. Open the request.csv file in VS Code and examine it. Notice that each row contains only two values, a product number and a quantity. Notice also that product number D083 appears twice in the file. It appears twice because the customer who created the order in the request.csv file added four yogurts to his order and then later added three more yogurts to his order. Because product numbers may appear multiple times in the request.csv file, your program must not read the contents of request.csv into a dictionary.
6. In your receipt.py program, write another function named main that does the following:

   1. Calls the read_dictionary function and stores the compound dictionary in a variable named products_dict.
   2. Prints the products_dict.
   3. Opens the request.csv file for reading.
   4. Skips the first line of the request.csv file because the first line contains column headings.
   5. Uses a loop that reads and processes each row from the request.csv file. Within the body of the loop, your program must do the following for each row:

      1. Use the requested product number to find the corresponding item in the products_dict.
      2. Print the product name, requested quantity, and product price.
7. At the bottom of your receipt.py file, add a call to the main function. Be certain to protect the call to main with an if statement as taught in the preparation content for lesson 5.

Testing Procedure

Verify that your program works correctly by following each step in this testing procedure:

1. Download the test_products.py file and save it in the same folder where you saved your receipt.py program. Run the test_products.py file and ensure that the test_read_dictionary function passes. If it doesn’t pass, there is a mistake in your read_dictionary function. Read the output from pytest, fix the mistake, and run the test_products.py file again until the test function passes.

   > python test_products.py
   =================== test session starts ====================
   platform win32--Python 3.8.6, pytest-6.1.2, py-1.9.0, pluggy
   rootdir: C:\Users\cse111\lesson09
   collected 1 item
   
   test_products.py::test_read_dictionary PASSED         [100%]
   
   ==================== 1 passed in 0.12s =====================

2. Run your program and verify that it prints the products dictionary and requested items as shown in the sample output below.

   > python receipt.py
   
   All Products
   {'D150': ['D150', '1 gallon milk', '2.85'], 'D083': ['D083',
   '1 cup yogurt', '0.75'], 'D215': ['D215', '1 lb cheddar
   cheese', '3.35'], 'P019': ['P019', 'iceberg lettuce',
   '1.15'], 'P020': ['P020', 'green leaf lettuce', '1.79'],
   'P021': ['P021', 'butterhead lettuce', '1.83'], 'P025':
   ['P025', '8 oz arugula', '2.19'], 'P143': ['P143', '1 lb
   baby carrots', '1.39'], 'W231': ['W231', '32 oz granola',
   '3.21'], 'W112': ['W112', 'wheat bread', '2.55'], 'C013':
   ['C013', 'twix candy bar', '0.85'], 'H001': ['H001', '8
   rolls toilet tissue', '6.45'], 'H014': ['H014', 'facial
   tissue', '2.49'], 'H020': ['H020', 'aluminum foil', '2.39'],
   'H021': ['H021', '12 oz dish soap', '3.19'], 'H025':
   ['H025', 'toilet cleaner', '4.50']}
   
   Requested Items
   wheat bread: 2 @ 2.55
   1 cup yogurt: 4 @ 0.75
   32 oz granola: 1 @ 3.21
   twix candy bar: 2 @ 0.85
   1 cup yogurt: 3 @ 0.75

Common Mistake

Counting Only Three D083 Yogurts

Because product number D083 appears twice in the request.csv file, your program must not read the request.csv file into a dictionary. Recall that each key in a dictionary is unique. If your program reads the request.csv file into a dictionary, when your program reads line 3 of the request.csv file, your program will put a request for four yogurts into the dictionary. Then when your program reads line 6 of the request.csv file, your program will replace the request for four yogurts with a request for three yogurts. In other words, if your program reads the request.csv file into a dictionary, your program will think that the customer ordered only three yogurts instead of the seven (4 + 3) that he ordered. Therefore, your program must not read the request.csv file into a dictionary but should instead read and process each row similar to example 3 in the preparation content for this lesson.

Submission

On or before the due date, return to I‑Learn and report your progress on this milestone.