✅ Objectives

• Learn about decorators
  • what are they?
  • how are they useful in Python classes?
  • Python’s “pie” syntax
• Understand class variables
  • how to define and update their value
• Write class methods
  • use the @classmethod decorator
  • cls keyword

• Object inheritance
  • how is it useful?
  • inherited or overwritten?
  • calling super()

• Build one-to-many relationships between objects
  • Discuss their importance and use
  • Emphasize single-source-of-truth
  • Demonstrate building one-way and two-way relationships
• Build many-to-many relationships between objects
  • Discuss their importance and use
  • Demonstrate building the relationship with and without intermediary class
• Aggregate Methods
  • Write aggregate methods to collect data about objects using their related objects

      class Pet:
        total_pets = 0
        all = []
    

• class variables are espcially useful for tracking cumulative data about all of the objects instantiated
• a list can even be used to keep a reference to every object itself!

      class Pet:
        total_pets = 0
        all = []
        @classmethod
        def add_to_total_pets(cls):
          cls.total_pets += 1
    

      Pet.add_to_total_pets()
    

• Just as we can give a class attributes with class variables, we can also give it behavior with class methods.
• these methods often update the values of the class variables in some way

Let's get hacking! 🕶️

Method overriding

class Vehicle:
    def vehicle_info(self):
        print("Inside Vehicle Class")

    def max_speed(self):
        print("max speed is 100 Km/Hour")


class Car(Vehicle):
    def car_info(self):
        print("Inside Car Class")

    # overridden the implementation of Vehicle class
    def max_speed(self):
        print("max speed is 200 Km/Hour")

# Creating object of Car class
car = Car()
car.vehicle_info() # => "Inside Vehicle Class"
car.car_info() # => "Inside Car Class"
car.max_speed() # => "max speed is 200 Km/Hour"

super() method

The super function returns a temporary object of the parent class that allows us to call a parent class method inside a child class method.

Benefits of using the super() function

• We are not required to remember or specify the parent class name to access its methods.
• We can use the super() function in both single and multiple inheritances.
• The super() function support code reusability as there is no need to write the entire function

class Company:
    def company_name(self):
        return 'Google'

class Employee(Company):
    def info(self):
        # Calling the superclass method using super()function
        c_name = super().company_name()
        print("Jessa works at", c_name)

# Creating object of child class
emp = Employee()
emp.info()

Let’s do it! 🏃‍♂️