Welcome to your next step in mastering Clean Code! 🚀 Previously, we emphasized the significance of naming conventions in clean coding. Now, we delve into the realm of functions and methods, which serve as the backbone of application logic and are crucial for code organization and execution. Structuring these functions effectively is vital for enhancing the clarity and maintainability of a codebase. In this lesson, we'll explore best practices and techniques to ensure our code remains clean, efficient, and readable.

Let's outline the key principles for writing clean functions:

• Keep functions small. Small functions are easier to read, comprehend, and maintain.
• Focus on a single task. A function dedicated to one task is more reliable and simpler to debug.
• Limit arguments to three or fewer. Excessive arguments complicate the function signature and make it difficult to understand and use.
• Avoid boolean flags. Boolean flags can obscure the code's purpose; consider separate methods for different behaviors.
• Eliminate side effects. Functions should avoid altering external states or depending on external changes to ensure predictability.
• Implement the DRY principle. Employ helper functions to reuse code, minimizing redundancy and enhancing maintainability.

Now, let's take a closer look at each of these rules.

Functions should remain small, and if they become too large, consider splitting them into multiple, focused functions. While there's no fixed rule on what counts as large, a common guideline is around 15 to 25 lines of code, often defined by team conventions.

Below, you can see the process_order function, which is manageable but has the potential to become unwieldy over time:

Given that this process involves multiple steps, it can be improved by extracting each step into a dedicated function, as shown below:

In this code block, the process_order function orchestrates the whole order processing operation. It first validates the order and attempts payment processing. If either step fails, the function logs an error and returns early. Successful orders trigger the inventory update, customer notification, and finally, a success log entry.

In this code block, we define helper functions for each individual step in the order processing pipeline. validate_order checks the validity of the order, while process_payment handles the payment execution. Both functions log any failures. After these checks, update_inventory adjusts the stock levels, notify_customer communicates with the client, and log_order_processing captures a success message for completed orders.

A function should embody the principle of doing one thing only. If a function handles multiple responsibilities, it may include several logical sections. Below you can see the save_and_notify_user function, which is both too lengthy and does multiple different things at once:

To enhance this code, you can create two dedicated functions for saving the user and sending the welcome email. This results in dedicated responsibilities for each function and clearer coordination:

Here we define save_and_notify_user, which coordinates saving a user to the database and subsequently notifying them. It calls two separate functions to achieve these tasks, promoting clear separation of responsibilities.

In this code block, save_user handles database operations related to saving user data and manages any exceptions that arise. notify_user is responsible for sending notifications, using the send_welcome_email method, which contains the logic for email dispatch.

Try to keep the number of function arguments to a maximum of three, as having too many can make functions less understandable and harder to use effectively. 🤔

Consider the save_address function below with five arguments, which makes the function less clean:

A cleaner version encapsulates the details into an Address object, reducing the number of arguments and making the function signature clearer:

Here is what an Address class might look like:

Boolean flags in functions can create confusion, as they often suggest multiple pathways or behaviors within a single function. Instead, use separate methods for distinct behaviors.

The set_flag function below uses a boolean flag to indicate user status, leading to potential complexity:

A cleaner approach is to have distinct methods representing the different behaviors:

A side effect occurs when a function modifies some state outside its scope or relies on something external. This can lead to unpredictable behavior and reduce code reliability.

Below, the add_to_total function demonstrates a side effect by modifying an external state:

A cleaner version, calculate_total, performs the operation without altering any external state:

Avoid code repetition by introducing helper functions to reduce redundancy and improve maintainability.

The print_user_info and print_manager_info functions below repeat similar logic, violating the DRY principle:

To adhere to DRY principles, use a generalized print_info function that operates on a parent Person type:

In this lesson, we learned that clean functions are key to maintaining readable and maintainable code. By keeping functions small, adhering to the Single Responsibility Principle, limiting arguments, avoiding side effects, and embracing the DRY principle, you set a strong foundation for clean coding. Next, we'll practice these principles to further sharpen your coding skills! 🎓