Table of Contents(目次)
What You Will Learn in This Section
In this section, you will learn about classes in Python.
Simply put, a class is like a "blueprint that combines data and behavior." Based on this blueprint, you can create actual objects (instances) that hold their own unique information.
Why Classes Are Important
When writing programs, you will often encounter situations where you need to reuse the same kind of data or logic multiple times. For example, imagine you are building a car simulation program.
- Every car has common actions like “drive” and “brake.”
- Each car has its own information such as “color,” “speed,” and “brand.”
In such cases, it would be inefficient to write similar code and data separately for every car type or color. Using a class allows you to centralize the shared design, which improves reusability and reduces bugs. You can think of writing a “car design” in a class, and then creating specific cars like Prius or Corolla as instances based on that design.
What You Will Learn in Each Lesson
Here’s what you will study throughout this section.
Understanding Classes and Instances
In this lesson, you’ll first learn the difference between a class and an instance. A class serves as a blueprint, and instances are the actual objects created from that blueprint, containing the data and behavior defined in the class.
For example, if you define a Car class, you can create specific cars such as “Prius” or “Corolla” as instances based on that blueprint. You’ll also learn how to define variables and behaviors unique to each instance using keywords like self and __init__. This helps you visualize the relationship between a class design and the objects created from it.
Mastering Class Variables and Class Methods
In this lesson, you’ll understand the difference between class variables and instance variables and learn how to use each properly. A class variable is shared across all instances of a class, making it useful for managing information such as a “universal tire size” or “total number of cars sold.” In contrast, instance variables hold data specific to each object, like “individual car color” or “fuel level.”
You will also learn how to use @classmethod and @staticmethod to define methods that operate on the class as a whole or utility methods that do not depend on any instance. Additionally, you’ll be introduced to the concept of factory methods — special methods designed to make it easier to create new instances.
Expanding Class Design with Inheritance and Overriding
Here, you’ll learn about inheritance, a powerful concept that makes class design more efficient. It allows you to group shared logic in a parent class and extend or override it in child classes as needed.
For instance, you can define a Car class that contains common methods like “drive” and “brake.” Then, child classes such as ElectricCar and GasCar can inherit these features from Car. You can also add or modify behaviors for specific needs. Using super() lets you call methods from the parent class, improving both reusability and flexibility of your code.
Special Methods, Encapsulation, and Properties
In this lesson, you’ll explore techniques to make classes more powerful and secure.
Special Methods: By defining methods like __str__ and __eq__, you can easily control how objects are represented and compared.
Encapsulation: By prefixing attribute names with _ or __, you can prevent unintended external access, protecting your internal data.
Properties: With @property, you can handle both getting and setting values through the same method name, allowing for safe internal control while keeping the external interface simple.
Constructors and Destructors: A constructor (__init__) runs once when an instance is created, performing initialization or setup. A destructor (__del__) runs once when an object is destroyed, handling cleanup or resource release. For example, in a class that manages network connections, __init__ might open a connection while __del__ safely closes it.
Documenting Classes with Docstrings
In this lesson, you’ll learn about Docstrings, which are used to document your classes and methods. Writing Docstrings helps you and others quickly understand how to use a class and what it was designed for. They can appear in IDEs (like Visual Studio Code’s autocomplete) or when using help(), greatly improving code readability and maintainability.
Finally, you’ll review all the concepts and techniques covered in this section, gaining hands-on experience in designing classes that are clear, effective, and maintainable.
