Object-oriented Programming

Object-oriented Programming#

Structure of object-oriented programming#

Classes#

  • User-defined data types

  • Blueprint for objects, attributes, and methods

  • Let’s define a class Person with the attributes age and name:

class Person:
    def __init__(self, name, age):
        self.name = name
        self.age = age

Objects#

  • Instance of a class with specifically defined data

  • Can correspond to real-world objects

  • Let’s create an instance of the class Person:

p = Person(age=29, name="Veit")

Methods#

  • Functions that objects can perform

  • Describe behaviors of an object

  • Defined inside the class

  • Let’s add a method that determines if the person is an adult:

class Person:
    def __init__(self, name, age):
        self.name = name
        self.age = age

    def is_adult(self):
        return self.age >= 18

Attributes#

  • Represent state of an object

  • Defined inside the class

  • Let’s print the attributes of the instance p:

print(p.name)  # Output: Veit
print(p.age)   # Output: 29

Inheritance and composition#

Inheritance#

  • Inheritance lets one class reuse or extend the behavior of another class

  • You create a child class (derived class) that inherits attributes and methods from a parent class (base class)

class Animal:
    def speak(self):
        return "Some sound"


class Dog(Animal):
    def speak(self):
        return "Woof!"


dog = Dog()
print(dog.speak())  # Output: Woof!

  • Dog inherits from Animal and overrides the speak() method

  • Is a relationship: Dog is a specialized version of Animal

Composition#

  • Composition means building complex objects by combining simpler ones

  • Instead of inheriting, a class has instances of other classes as attributes

  • This means that a class Composite can contain an object of another class as Component

class Engine:
    def start(self):
        return "Engine started"


class Car:
    def __init__(self):
        self.engine = Engine()

    def start(self):
        return self.engine.start()


car = Car()
print(car.start())  # Output: Engine started

  • Car has an Engine, and it uses the engine’s method to start

  • has a relationship: Car has a component Engine

Sources#

Contents