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Python Objects

Introduction to Objects

Objects in Python represent an encapsulation of variables (properties) and functions (methods) into a single entity. Objects are created from classes, which can be thought of as blueprints for the object.

Basic Concepts

  • Object: An instance of a class containing properties and methods.
  • Class: A blueprint for creating objects, providing initial values for properties, and implementations of methods.

Example

class Car:
    def __init__(self, brand, model, year):
        self.brand = brand
        self.model = model
        self.year = year

    def display_info(self):
        print(f"This is a {self.year} {self.brand} {self.model}")

my_car = Car("Ford", "Mustang", 1964)
my_car.display_info()

Properties

Properties are variables that belong to an object.

Example

print(my_car.brand)  # Accessing the 'brand' property of the 'my_car' object

Methods

Methods are functions that belong to an object.

Example

my_car.display_info()  # Calling the 'display_info' method of the 'my_car' object

Class Definition

Basic Structure

A class is defined using the class keyword, followed by the class name and a colon.

Syntax

class ClassName:
    # properties and methods

The __init__ Method

The __init__ method is a special method called a constructor, used for initializing properties of an object.

Syntax

class ClassName:
    def __init__(self, parameter1, parameter2):
        self.property1 = parameter1
        self.property2 = parameter2

Object-Oriented Concepts

Inheritance

Inheritance allows a new class to extend an existing class, inheriting its properties and methods.

Example

class ElectricCar(Car):
    def __init__(self, brand, model, year, battery_size):
        super().__init__(brand, model, year)
        self.battery_size = battery_size

Encapsulation

Encapsulation involves restricting access to properties and methods, often using private and protected access modifiers.

Polymorphism

Polymorphism allows methods to do different things based on the object it is acting upon.

Class and Instance Variables

  • Class variables are shared by all instances of a class.
  • Instance variables are unique to each instance.

Example

class Dog:
    species = "Canis familiaris"  # Class variable

    def __init__(self, name, age):
        self.name = name  # Instance variable
        self.age = age    # Instance variable

Recap

Concept Description Example
Class Blueprint for creating objects class Dog: pass
Object An instance of a class my_dog = Dog()
Properties Variables belonging to an object my_dog.name = 'Rex'
Methods Functions belonging to an object def bark(self): print("Woof!")
Inheritance Extending the functionality of a class class Bulldog(Dog): pass
Encapsulation Restricting access to properties and methods Using _ or __ to denote private/protected attributes
Polymorphism Methods can act differently based on the object type Overriding methods in child classes
Class Variable Variable shared by all instances of a class Dog.species = 'Canis familiaris'
Instance Variable Unique to each instance self.name = name in the __init__ method

Best Practices

  • Use proper naming conventions (CamelCase for classes, lowercase_with_underscores for functions and variables).
  • Keep class definitions simple and focused on a single responsibility.
  • Document classes and methods clearly for maintainability.