The provided Python code defines a basic inventory management system....

May 18, 2025 at 11:44 AM

from datetime import datetime
import write  

def add_product(products, filename, product_name):
    print(f"\n=== Add New Product: {product_name} ===")
    # Use the provided product name
    if any(p['name'].lower() == product_name.lower() for p in products):
        print(f"Product '{product_name}' already exists in inventory.")
        return False
        
    brand = input("Enter brand name: ").strip()
    if not brand:
        print("Brand name required and cannot be empty.")
        return False
        
    country = input("Enter country of origin: ").strip()
    if not country:
        print("Country is required and cannot be empty.")
        return False
        
    try:
        quantity = int(input("Enter initial quantity: "))
        if quantity < 0:
            print("Quantity must be a non-negative number.")
            return False
            
        cost_price = float(input("Enter cost price: "))
        if cost_price < 0:
            print("Cost price must be a non-negative number.")
            return False
            
    except ValueError:
        print("Invalid input. Please enter valid numbers for quantity and cost price.")
        return False
        
    new_product = {
        'name': product_name,
        'brand': brand,
        'quantity': quantity,
        'cost_price': cost_price,
        'country': country
    }
    
    products.append(new_product)
    write_to_file(filename, products)
    print(f"Product '{product_name}' successfully added to stock.")
    return True

def write_to_file(filename, products):
    try:
        with open(filename, 'w') as file:
            for product in products:
                line = f"{product['name']},{product['brand']},{product['quantity']},{product['cost_price']},{product['country']}\n"
                file.write(line)
        print(f"{filename} has been successfully updated.")
    except PermissionError:
        print(f"Error: Permission denied when writing to {filename}.")
    except Exception as e:
        print(f"Error writing to file: {e}")

def process_transaction(products, filename):
    if not products:
        print("No products available for transactions at the moment.")
        return
    customer_name = input("Enter customer name: ").strip()
    if not customer_name:
        print("Customer name is required and cannot be left blank.")
        return
    transaction = []
    while True:
        write.display_products(products)  
        product_name = input("Enter product name (or 'done' to finish): ").strip()
        if product_name.lower() == 'done':
            break
        product = next((p for p in products if p['name'].lower() == product_name.lower()), None)
        if not product:
            print(f"Sorry, the product '{product_name}' is not in stock.")
            add_choice = input("Do you want to add this product to the Stock? (yes/no): ").strip().lower()
            if add_choice == 'yes':
                if add_product(products, filename, product_name):
                    # Refresh product reference after adding
                    product = next((p for p in products if p['name'].lower() == product_name.lower()), None)
                else:
                    continue
            else:
                continue
        try:
            qty = int(input(f"Enter quantity to purchase for {product['name']}: "))
            if qty <= 0:
                print("Please enter a valid positive quantity.")
                continue
            free_items = qty // 3  # Buy 3 get 1 free
            total_items = qty + free_items
            if total_items > product['quantity']:
                print(f"We currently have insufficient stock for {product['name']}. Available: {product['quantity']}, Requested: {total_items}.")
                continue
            try:
                selling_price = product['cost_price'] * 2
            except KeyError as e:
                print(f"Error: Missing key {e} in product data.")
                continue
            transaction.append({
                'product': product,
                'qty_purchased': qty,
                'free_items': free_items,
                'VAT': 0.13 * (qty * selling_price),
                'total_cost': qty * selling_price + 0.13 * (qty * selling_price)
            })
        except ValueError:
            print("Invalid input. Please provide a numeric value for quantity.")
            continue
    if not transaction:
        print("No items were purchased during this transaction.")
        return
    for item in transaction:
        product = item['product']
        product['quantity'] -= (item['qty_purchased'] + item['free_items'])
    timestamp = datetime.now().strftime("%Y%m%d_%H%M%S")
    invoice_filename = f"invoice_{timestamp}.txt"
    total_amount = sum(item['total_cost'] for item in transaction)
    try:
        with open(invoice_filename, 'w') as file:
            file.write("=== Sales Invoice ===\n")
            file.write(f"Customer: {customer_name}\n")
            file.write(f"Date: {datetime.now().strftime('%Y-%m-%d %H:%M:%S')}\n")
            file.write("-" * 40 + "\n")
            file.write(f"{'Product':<20} {'Brand':<15} {'Qty':<10} {'Free':<10} {'VAT': <8} {'Cost':<15}\n")
            file.write("-" * 40 + "\n")
            for item in transaction:
                product = item['product']
                file.write(f"{product['name']:<20} {product['brand']:<15} {item['qty_purchased']:<10} {item['free_items']:<10} {item['VAT']:<8} {item['total_cost']:<15.2f}\n")
            file.write("-" * 40 + "\n")
            file.write(f"Total Amount: {total_amount:.2f}\n")
        print(f"Invoice successfully created: {invoice_filename}")
    except Exception as e:
        print(f"Error generating invoice: {e}")
    write_to_file(filename, products)

def restock_products(products, filename):
    if not products:
        print("No products are available for restocking.")
        return
    supplier_name = input("Enter supplier name: ").strip()
    if not supplier_name:
        print("Supplier name is mandatory and cannot be empty.")
        return
    write.display_products(products)  
    product_name = input("Enter product name to restock: ").strip()
    product = next((p for p in products if p['name'].lower() == product_name.lower()), None)
    if not product:
        print(f"The product '{product_name}' could not be located in the inventory.")
        return
    try:
        qty = int(input(f"Enter quantity to restock for {product['name']}: "))
        if qty <= 0:
            print("Please enter a valid positive number for the quantity.")
            return
        cost_price = float(input(f"Enter new cost price for {product['name']} (current: {product['cost_price']}): "))
        if cost_price < 0:
            print("Cost price must be a non-negative value.")
            return
    except ValueError:
        print("Invalid input. Please enter valid numbers.")
        return
    product['quantity'] += qty
    product['cost_price'] = cost_price
    timestamp = datetime.now().strftime("%Y%m%d_%H%M%S")
    invoice_filename = f"restock_{timestamp}.txt"
    total_amount = qty * cost_price 
    try:
        with open(invoice_filename, 'w') as file:
            file.write("=== Restock Invoice ===\n")
            file.write(f"Supplier: {supplier_name}\n")
            file.write(f"Date: {datetime.now().strftime('%Y-%m-%d %H:%M:%S')}\n")
            file.write("-" * 40 + "\n")
            file.write(f"{'Product':<20} {'Brand':<15} {'Qty':<10} {'Cost':<15}\n")
            file.write("-" * 40 + "\n")
            file.write(f"{product['name']:<20} {product['brand']:<15} {qty:<10} {total_amount:<15.2f}\n")
            file.write("-" * 40 + "\n")
            file.write(f"Total Amount: {total_amount:.2f}\n")
        print(f"Restock invoice successfully created: {invoice_filename}")
    except Exception as e:
        print(f"Error generating restock invoice: {e}")
    write_to_file(filename, products)

The provided Python code defines a basic inventory management system. Here's what each part of the code does:

`add_product(products, filename, product_name)`

This function adds a new product to the inventory.

Checks if the product already exists: Searches the products list for a product with a matching name (case-insensitive).
Prompts for information: If the product doesn't already exist, the user is prompted to enter details like brand, country of origin, initial quantity, and cost price. Validation ensures inputs are non-empty and numeric values are valid.
Adds the product to the inventory: The new product, structured as a dictionary, is appended to the products list.
Writes the updated inventory to file: The write_to_file function is called to save the updated products list to the specified file.

`write_to_file(filename, products)`

This function writes the current state of the inventory (products list) to a file in CSV format.

Each product is saved as a line with its properties (name, brand, quantity, cost_price, and country).
Includes error handling for issues such as permission errors or other unexpected exceptions during file writing.

`process_transaction(products, filename)`

This function handles customer transactions (purchasing products).

Validates inventory and customer input: Ensures the product list is not empty and prompts for the customer's name.
Handles product selection and purchase: For each product the customer wants to buy:
- Finds the product in the inventory (or prompts to add it if it doesn't exist).
- Validates quantities (checks stock availability) and calculates the free items (based on a "Buy 3, Get 1 Free" promotion).
- Calculates the selling price, VAT (13%), and total cost.
- Records the transaction if everything is valid.
Deducts purchased quantities from stock: Updates the products list.
Generates an invoice: Creates a text file with the transaction details, including the purchased products, their quantities, VAT, and the total price.
Updates inventory file: Writes the updated inventory back to the file.

`restock_products(products, filename)`

This function restocks an existing product in the inventory.

Validates existing products: Ensures the inventory is not empty and the supplied product exists.
Prompts for supplier information: The user enters the supplier name, restock quantity, and updated cost price. Validation is performed for numerical inputs and non-negative values.
Updates the selected product: Adds the restocked quantity to the product and updates its cost price.
Generates a restock invoice: Saves the restock details to a file (including supplier name, product details, and total cost).
Updates inventory file: Saves the modified inventory list to the file.

Supporting Functionalities:

Error Handling: The code handles errors like invalid inputs, missing keys in product data, file access permissions, or unexpected exceptions during file I/O.
Integration with write Module: The code references the write module to access functions like display_products, which lists the inventory items for user interaction.

Key Observed Behaviors:

Buy 3, Get 1 Free Promotion: Ensures customers receive a free product for every 3 purchased, but only if there is sufficient stock (total calculated items, purchased plus free, must not exceed inventory quantity).
Invoice and Restock File Generation: The application creates transaction logs in a timestamped file for reference or bookkeeping.
Real-Time Inventory Update: Modifies the shared products list to reflect transactions or restocking immediately.

The code provides a basic framework for managing a stock inventory system with functionalities for adding products, processing transactions (with a promotion), and restocking items.

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