Functions with no Return

Functions without a return statement are helpful when you want to structure your code into reusable sections that perform tasks like printing messages, modifying data, or executing actions within your program.

Note

In Python, every function returns a value. If a function doesn't explicitly include a return statement, it will automatically return None.

Let's see how Alex demonstrates the creation and use of functions that don't return a value:

The best way to understand how we use functions with no return statement is to see them in action, so let's look at some examples.

Printing Information to the Console

Sometimes, the purpose of a function is simply to notify the user of a specific event or outcome by printing information to the console.

For example, there's no need to return a value in the total_sales() function because its primary role is to perform a calculation and display the result immediately:


              1234567
            
# Prices of items sold today
prices = [12.99, 23.50, 4.99, 8.75, 15.00]

def total_sales(prices):
    print(f"Today's total sales: $", sum(prices))

total_sales(prices)

Note

The order in which data and functions are declared doesn't matter. The only important rule is that a function must be defined before it is called.

Modifying a Data Structure

Developers often need to create functions that modify a data structure, like a list or dictionary, without returning a value.

For instance, the update_inventory() function adjusts inventory levels based on the items_sold. Since the function modifies the inventory dictionary directly, there's no need to return anything:


              12345678910111213141516171819202122232425
            
# Define the function that adjusts inventory levels
def update_inventory(inventory, items_sold):
    # Iterate over each item in the dictionary
    for product, quantity_sold in items_sold.items():
        # Decrease the inventory by the quantity sold for each product
        inventory[product] -= quantity_sold

# Inventory dictionary
inventory = {
    "apples": 50,
    "bananas": 75,
    "oranges": 100
}

# Items sold dictionary
items_sold = {
    "apples": 5,
    "oranges": 15
}

# Update the inventory based on items sold
update_inventory(inventory, items_sold)

# Display the updated inventory
print("Updated inventory:", inventory)

Calling Another Function

It's common to create functions that monitor specific conditions and trigger other functions when needed.

For example, the check_stock_levels() function checks if any product's stock level drops below a set threshold. If so, it calls the restock() function to order more inventory.

This approach doesn't require returning a value, as the main goal is to initiate the restocking process:


              12345678910111213141516171819202122232425
            
# Dictionary representing the current stock of products
inventory = {
    "apples": 17,
    "bananas": 75,
    "oranges": 2,
    "grapes": 50
}

# Function to restock items that have low stock levels by adding a specified amount
def restock(product, inventory, restock_amount):
    inventory[product] += restock_amount
    print(f"Restock order placed for {product}. New stock level: {inventory[product]} units.")

# Function to check which items are below the stock threshold and trigger the `restock` function
def check_stock_levels(inventory, threshold):
    for product, quantity in inventory.items():
        if quantity < threshold:
            # If the stock is below the threshold, call the `restock` function to add 50 units
            restock(product, inventory, 50)

# Checking the stock levels for all products in the inventory with a threshold of 30 units
check_stock_levels(inventory, 30)

# Display the final inventory after restocking
print("Final inventory status:", inventory)

Everything was clear?

Thanks for your feedback!

Section 6. Chapter 5