Master Python OOP: From Real‑World Thinking to Classes and Objects

1. Introduction to Object‑Oriented Programming

In real life we think about a student introducing themselves, not the act of introduction first. This contrasts with code where the behavior is written before deciding who it applies to.

How to express our real‑world thinking in code?

Procedural programming: write code top‑down according to business logic.

Object‑oriented programming: bind data and functions together, encapsulate, enabling faster development and reducing duplicate code.

Today we learn a new programming paradigm: Object‑Oriented Programming (OOP).

Two very important OOP concepts: class and object.

An object is the core of OOP; to group objects with common features we define a class.

A class is like a blueprint for creating objects (e.g., a plane).

2. Analyzing Classes and Objects

1. Class

物以类聚，人以群分。
具有相似内部状态和运动规律的实体的集合(或统称为抽象)。
具有相同属性和行为事物的统称。

Classes are abstract; we instantiate them to obtain concrete objects. One class can produce many objects.

2. Object

# 某一个具体事物的存在 ,在现实世界中可以是看得见摸得着的。
# 可以是直接使用的

3. Relationship between Class and Object

Summary: a class is a template for creating objects.

4. Distinguishing Classes and Objects

# 奔驰smart 类
# 张三的那辆奔驰smart 对象
# 水果 类
# 苹果 类
# 红苹果 类 红富士苹果 类
# 我嘴里吃了一半的苹果 对象

5. Components of a Class

A class consists of three parts:

Class name.

Attributes: a set of data.

Methods: operations that can be performed on objects.

Example:

1) Human design focuses on three things:

Class name: Person.

Attributes: height, age.

Methods: run, fight.

2) Dog class design:

Class name: Dog.

Attributes: breed, color, gender, name, number of legs.

Methods: bark, run, bite, eat, wag tail.

6. Class Abstraction

How to abstract everyday things into program classes? Objects sharing similar attributes and behaviors can be abstracted into a class. Usually nouns become class names.

1) Tank fires three shells, destroys two planes

Tank → class.

Shell → class.

Plane → class.

2) Xiao Ming on a bus holding a dog with a hot dog

Xiao Ming → Person class.

Bus → Vehicle class.

Hot dog → Food class.

Dog → Dog class.

3) Identify classes in the diagram

Explanation: Person, Gun, Bullet, Grenade, Knife, Box.

4) Identify classes in another diagram

Explanation: Sunflower (class xrk, attributes color, type, behavior expose sunlight), Pea (class wd, attributes color, hairstyle, health, behavior fire, shake head), Nut (class jg, attributes health, type, behavior block), Zombie (class js, attributes color, health, type, speed, behavior walk, run jump, eat, die).

3. Project

1. Define a Class

Define a class with the following format:

class ClassName:
    # method list

Demo: define a Cat class

# Define class
class Cat:
    # method
    def eat(self):
        print("猫在吃鱼....")
    def drink(self):
        print("猫在喝可乐...")

Note: there are new‑style and classic classes; Cat above is classic. Naming follows PascalCase.

2. Create an Object

In Python, create objects from a defined class: object_name = ClassName() Demo:

# Define a class
class Cat:
    def eat(self):
        print("猫在吃鱼....")
    def drink(self):
        print("猫在喝可乐...")
# Create an object
tom = Cat()

3. Call Object Methods

class Cat:
    def eat(self):
        print("猫在吃鱼....")
    def drink(self):
        print("猫在喝可乐...")

tom = Cat()
tom.eat()
tom.drink()

Result shown in image:

4. Add Attributes to an Object

class Cat:
    def eat(self):
        print("猫在吃鱼....")
    def drink(self):
        print("猫在喝可乐...")

tom = Cat()
# Add attributes
tom.name = "汤姆"
tom.age = 30

tom.eat()
tom.drink()
print(tom.name)
print(tom.age)

Result shown in image:

5. Access Object Attributes via Methods

class Cat:
    def eat(self):
        print("猫在吃鱼....")
    def drink(self):
        print("猫在喝可乐...")
    def introduce(self):
        print("名字是:%s, 年龄是:%d" % (tom.name, tom.age))

tom = Cat()
# Add attributes
tom.name = "汤姆"
tom.age = 30

tom.eat()
tom.drink()
print(tom.name)
print(tom.age)
print("-"*30)
# Call method that accesses attributes
 tom.introduce()

Result shown in image:

4. Summary

This article uses everyday phenomena to introduce Python OOP basics, offering rich examples to help readers understand objects, and concludes with a small cat project to reinforce class and object concepts.