Welcome back! You've learned so much about creational patterns, and it's time to apply what you know to a real-world project: a banking system. In this unit, we'll focus on using creational patterns to manage and simplify the creation of banking system components.

Before we dive in, let's quickly recap the creational patterns we'll use:

1. Singleton Pattern: Ensures a class has only one instance and provides a global point of access to it.
2. Factory Method Pattern: Defines an interface for creating an object but allows subclasses to alter the type of objects that will be created.
3. Abstract Factory Pattern: Provides an interface for creating families of related or dependent objects without specifying their concrete classes.
4. Builder Pattern: Separates the construction of a complex object from its representation, allowing the same construction process to create various representations.

We will implement these patterns to create a logger, accounts, and account factories for our banking system.

Let's see what you'll build in this unit. You will create:

1. Logger with the Singleton Pattern: A logging mechanism that ensures only one instance of the logger exists throughout the application.
2. Accounts using the Factory Method Pattern: Different types of accounts (savings and current) created via a factory method.
3. Account Factories using the Abstract Factory Pattern: Factories that will instantiate different types of accounts.
4. Code Integration: Comprehensive integration of these patterns into a cohesive system.

First, let's create a logger using the Singleton Pattern. This will ensure that there is only one instance of the logger throughout the application.

Here, the Logger class ensures that only one instance of the logger exists. Whenever a message needs to be logged, the single instance is used.

Next, we will create different types of accounts using the Factory Method Pattern. This will allow us to create specific types of accounts while adhering to a common interface.

In this example, Account is an abstract class with an account_type method that needs to be implemented by its subclasses. SavingsAccount and CurrentAccount provide specific implementations of the account_type method, returning messages to indicate their type.

Now, let's move on to the Abstract Factory Pattern to create account factories, which will instantiate different types of accounts and associated debit cards.

Here, AccountFactory is an abstract factory that defines the methods create_account and create_debit_card. SavingsAccountFactory and CurrentAccountFactory are concrete factories that override these methods to return instances of SavingsAccount and SavingsDebitCard, and CurrentAccount and CurrentDebitCard respectively.

To integrate these patterns into a cohesive system, let's see how the different components work together.

In this code, we create instances of SavingsAccountFactory and CurrentAccountFactory. We use these factories to create savings_account, savings_debit_card, current_account, and current_debit_card, respectively. Each component's type is logged using the logger.

Here's the complete code putting everything together:

Understanding creational patterns in the context of a banking system not only strengthens your coding skills but also demonstrates their utility in real-world applications. These patterns help you maintain code quality by ensuring your code is clean, modular, and easy to understand. They encourage reusability, allowing you to reuse common components across different parts of the system, and enhance flexibility by enabling changes and extensions with minimal impact on existing code. By mastering these patterns, you'll be equipped to build robust and scalable systems efficiently.