Class and Object Relationship

Classes define blueprints for creating objects. Objects possess attributes (state) and methods (behavior).

Implementing Object-Oriented Concepts

Class Definition

class Vehicle():
    pass

Object Instantiation

car = Vehicle()
print(car)  # Memory address

Self Parameter

class Vehicle():
    def start_engine(self):
        print("Engine started")
        print(self)

car = Vehicle()
print(car)  # Same address as self

Multiple Objects

vehicle1 = Vehicle()
vehicle2 = Vehicle()
# Different memory addresses

Object Attributes

Adding Attributes Externally

vehicle1.max_speed = 200
vehicle1.fuel_capacity = 50

Accessing Attributes Internally

class Vehicle():
    def display_specs(self):
        print(f"Max speed: {self.max_speed}")
        print(f"Fuel capacity: {self.fuel_capacity}")

vehicle1 = Vehicle()
vehicle1.max_speed = 200
vehicle1.fuel_capacity = 50
vehicle1.display_specs()

Special Methods

__init__ Method

class Vehicle():
    def __init__(self):
        self.max_speed = 180
        self.fuel_capacity = 45

Parameterized __init__

class Vehicle():
    def __init__(self, speed, capacity):
        self.max_speed = speed
        self.fuel_capacity = capacity

car = Vehicle(200, 50)

__str__ Method

class Vehicle():
    def __str__(self):
        return "Vehicle specifications"

car = Vehicle()
print(car)  # Vehicle specifications

__del__ Method

class Vehicle():
    def __del__(self):
        print("Object destroyed")

Inheritance

Single Inheritance

class Engine():
    def __init__(self):
        self.type = "V8"

class Car(Engine):
    pass

my_car = Car()
print(my_car.type)  # V8

Mulitple Inheritance

class ElectricMotor():
    def __init__(self):
        self.power_source = "Electric"

class CombustionEngine():
    def __init__(self):
        self.power_source = "Gasoline"

class HybridVehicle(ElectricMotor, CombustionEngine):
    pass

hybrid = HybridVehicle()
print(hybrid.power_source)  # Electric

Method Overriding

class HybridVehicle(ElectricMotor, CombustionEngine):
    def __init__(self):
        self.power_source = "Hybrid"
    
    def show_power(self):
        print(f"Power: {self.power_source}")

hybrid = HybridVehicle()
hybrid.show_power()  # Power: Hybrid

Accessing Parent Methods

class HybridVehicle(ElectricMotor, CombustionEngine):
    def show_electric(self):
        ElectricMotor.__init__(self)
        print(f"Source: {self.power_source}")
    
    def show_combustion(self):
        CombustionEngine.__init__(self)
        print(f"Source: {self.power_source}")

hybrid = HybridVehicle()
hybrid.show_electric()  # Source: Electric

Super() Function

class HybridVehicle(ElectricMotor):
    def __init__(self):
        super().__init__()
        # Additional initialization

Access Control

class Vehicle():
    def __init__(self):
        self.__vin = "ABC123"
    
    def get_vin(self):
        return self.__vin
    
    def set_vin(self, new_vin):
        self.__vin = new_vin

car = Vehicle()
print(car.get_vin())  # ABC123
car.set_vin("XYZ789")

OOP Principles

Encapsulation: Bundling data and methods within a class
Inheritance: Creating new classes from existing ones
Polymorhpism: Different objects responding to same method differently

Polymorphism Example

class PaymentMethod():
    def process_payment(self):
        pass

class CreditCard(PaymentMethod):
    def process_payment(self):
        print("Processing credit card")

class PayPal(PaymentMethod):
    def process_payment(self):
        print("Processing PayPal")

def execute_payment(method):
    method.process_payment()

card = CreditCard()
paypal = PayPal()
execute_payment(card)    # Processing credit card
execute_payment(paypal)  # Processing PayPal

Class vs Instance Attributes

class Vehicle():
    wheels = 4  # Class attribute

car = Vehicle()
bike = Vehicle()
print(Vehicle.wheels)  # 4
print(car.wheels)      # 4

Vehicle.wheels = 6
print(bike.wheels)     # 6

car.wheels = 2  # Creates instance attribute
print(car.wheels)      # 2
print(Vehicle.wheels)  # 6

Class and Static Methods

class Vehicle():
    @classmethod
    def class_info(cls):
        print("Vehicle class information")
    
    @staticmethod
    def static_info():
        print("Static vehicle info")

Vehicle.class_info()
Vehicle.static_info()