Question

A store owner keeps a record of daily cash transactions in a text file. Each line contains three items: The invoice number, the cash amount, and the letter P if the amount was paid or \(\mathrm{R}\) if it was received. Items are separated by spaces. Write a program that prompts the store owner for the amount of cash at the beginning and end of the day, and the name of the file. Your program should check whether the actual amount of cash at the end of the day equals the expected value.

Short answer

The program compares expected and actual end-of-day cash amounts after processing transactions from the file.

Step-by-step solution

Initialize the Program

Start by asking the store owner for the amount of cash at the beginning of the day, the amount at the end of the day, and the name of the file where transactions are recorded. These inputs can be taken using Python's `input()` function.

Open and Read the File

Open the file using Python's `open()` function in read mode. Iterate through each line of the file using a loop to process the transaction data.

Parse Transaction Data

For each line, split the line into its components: invoice number, cash amount, and type of transaction (P for paid, R for received). Use Python's `split()` function to break up the line by spaces.

Calculate Net Cash Change

Initialize a variable to track the net change in cash. For each transaction, if the line contains 'P', subtract the cash amount from net change. If it contains 'R', add the amount to the net change.

Determine Expected End-of-Day Cash

Calculate the expected amount of cash by adding the initial cash to the net change calculated from transactions. This gives the expected final cash balance.

Compare Actual vs. Expected Cash

Compare the expected end-of-day cash calculated in Step 5 with the actual end-of-day cash provided by the store owner. Use an if-else statement to print whether they match or differ.

Key concepts

Python input() function

When working with Python, gathering user input is often essential for interactive programs. This is where the `input()` function comes into play. It allows you to pause program execution and wait for the user to enter some data. Once the user provides the input and presses Enter, the program resumes.

The syntax for the `input()` function is straightforward:

• user_input = input("Prompt message here: ")

This captures what the user types and stores it in a variable. An important note is that `input()` always returns data as a string. If numerical input is needed, conversion (e.g., using `int()` or `float()`) is necessary.

In the context of the exercise, `input()` helps collect critical data from the store owner, like the initial and final cash amounts and the filename containing transaction records. It's important to validate this input to prevent errors and ensure smooth execution of your program.

Parsing text files in Python

Parsing text files allows you to extract and manipulate data efficiently. In Python, this involves opening a file, reading its contents, and breaking the information into manageable pieces.

The file is opened using the `open()` function, often in read mode (`'r'`). An example usage is:

• with open("filename.txt", 'r') as file:
•     contents = file.readlines()

Using `with` statement ensures the file is properly closed after its suite finishes, even if an error is raised at some point.

In our task, each line from the text file is a separate transaction that includes an invoice number, an amount, and a transaction type indicator. The `split()` function is useful here to divide each line into these components. It operates by splitting the line based on spaces:

• parts = line.split()

By iterating through lines and splitting them, the program can maticulously process each piece of transaction data for calculations.

Conditional statements in Python

Conditional statements, like `if`, `elif`, and `else`, are pivotal for decision-making in Python code. They help execute specific code blocks based on particular conditions, enabling your program to respond appropriately to various input scenarios.

The syntax for an `if-else` statement is generally as follows:

• if condition_1:     # Execute code for condition_1
• elif condition_2:     # Execute code for condition_2
• else:     # Execute code if neither condition above is true

In the exercise, conditional statements are crucial for determining if the actual end-of-day cash matches the expected cash based on transaction analysis. By comparing these values, the program can alert the user whether their account reconciles or if there's a discrepancy.

For example, you might use:

• if actual_cash == expected_cash:     print("Cash tallies perfectly!")
• else:     print("Discrepancy found!")

This enables clear, helpful output for the store owner and highlights Python's effective handling of conditional logic.