Quiz

In Python, an instance is an object created from a class.

class Dog:

    def __init__(self, name):

        self.name = name

    def bark(self):

        print(f"{self.name} says woof!")

# Create instances

dog1 = Dog("Buddy")

dog2 = Dog("Max")

print(dog1.name)   # Buddy

print(dog2.name)   # Max

dog1.bark()        # Buddy says woof!

In Python, there is no static keyword like in Java or C#, but the equivalent concept is a class variable (sometimes called a static property).

class Student:

    school = "ABC School"   # class variable

    def __init__(self, name):

        self.name = name    # instance variable

s1 = Student("Alice")

s2 = Student("Bob")

print(s1.school)  # ABC School

print(s2.school)  # ABC School

A class variable belongs to the class itself. There is only one copy shared by all instances.

An instance variable belongs to a particular object (instance). Each instance has its own copy.

"self" is the conventional variable name to refer to the class instance.

super() is used in inheritance to access methods or attributes from a parent class (superclass).

attribute: a quality or feature of somebody/something

Without super()

class Animal:

    def __init__(self, name):

        self.name = name

class Dog(Animal):

    def __init__(self, name, breed):

        self.name = name

        self.breed = breed

You have to duplicate the initialization logic.

With super()

class Dog(Animal):

    def __init__(self, name, breed):

        super().__init__(name)

        self.breed = breed

The parent class handles name, and the child class handles breed.

Assuming rover is an instance of a class Dog and speak() is an instance method, this line:

rover.speak()

is equivalent to calling the method through the class and explicitly (明確地) passing the instance as the first argument:

Dog.speak(rover)

In Python, instance methods automatically receive the object (self) as their first parameter. So:

class Dog:

    def speak(self):

        print("Woof!")

rover = Dog()

rover.speak()      # equivalent to:

Dog.speak(rover)

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