OOP-Cheatsheet

Core Concept of OOP

Lets talk about what is OOP in a layman language.

Imagine you're building a virtual world, like a video game or a simulation. In this world, everything can be thought of as objects. Objects are like characters or things that have characteristics (attributes) and can do things (methods).

Class: Class is a blueprint like how an object will behave. Objects: These are the main entities in your virtual world. For example, if you're creating a game, an object could be a player, an enemy, or a weapon.

Attributes: These are the characteristics or properties of the objects. For a player object, attributes might include the player's name, health, and score.

Methods: These are the actions or behaviors that objects can perform. In a game, a player object might have methods like "move," "attack," or "collect items."

Encapsulation: This is like putting things in a box. It means that an object keeps its attributes and methods together, and the outside world doesn't need to know all the details. For example, when you play a game, you don't need to know how the player's health is calculated; you just see the current health value.

Inheritance: This is like passing down traits in a family. One object can inherit attributes and methods from another object. For instance, if you have a general "character" object, a "player" object could inherit from it and add specific player-related features.

Polymorphism: This is like using the same word in different contexts. It allows different objects to be treated as instances of the same type. For example, both a player and an enemy might have a "damage" method, but they would behave differently.

Break Down Each of the concepts with code and example

Function vs Method:

Functions

• Definition: A function is a standalone block of code that performs a specific task. It is defined outside of any class or object.

• Usage: Functions can be called from anywhere in the code, as long as they are in the same scope or imported.

• Example:

  def add_numbers(a, b):
      return a + b
  
  result = add_numbers(5, 7)

Methods

• Definition: A method is a function associated with an object. It is defined within a class and is called on instances of that class.

• Usage: Methods are called on objects and operate on the data within those objects.

• Example:

  class Calculator:
      def add_numbers(self, a, b):
          return a + b
  
  calc = Calculator()
  result = calc.add_numbers(5, 7)

• Short Note: lets we have a list l and we want to find out length of this list.so we will write len(l) , but if we append something in a list we will write l.append(). cause len is a function and append, copy, pop,remove etc are a method of a list class.

Constructor

A constructor is like a setup wizard for objects in programming. It's a special method, often named __init__, that runs automatically when create an object. Its main job is to initialize the object's attributes or perform any necessary setup. In Python:

class MyClass  
    def __init__(self, initial_pin, initial_balance): 
    # this is constructor
     self.pin = initial_pin
     self.balance = initial_balance
    
my_object = MyClass("1234", 1000)

• Short Note:

• we usually write any sort of configuration related task in the constructor like database connectivity, hardware connectivity etc. so basically we dont want to give specific control to the user and that time we will use constructor.
  

• Inside Class only two things are possible one is data and other one is method. Only object of this class can access that data and method even one method can't access another method and its datas within the class. if one method is trying to access another method we need and object and as self is the current object so we can access if we use self and thats why we use self.

Simple Implementation based on our learning

Now let's write a code to understand oop better based on atm system

 class Atm:
   def __init__(self) :
       self.pin= ""
       self.balance=0
       self.menu()
       

   def menu(self):
       user_input= input(""" 
                        Hello, How would you like to proceed
                         1.Enter 1 to create pin
                         2.Enter 2 to deposit
                         3.Enter 3 to Withdraw
                         4.Enter 4 to check balance
                         5.Enter 5 to exit

                        """)
       if user_input=="1":
        self.create_pin()
       elif user_input=="2":
          self.deposit()
       elif user_input=="3":
          self.withdraw()
       elif user_input=="4":
          self.check_balance() 
       else:
          print("Bye")          
       

   def create_pin(self):
      self.pin=input("Enter your pin : ")
      print("Pin set sucessfully")

   def deposit(self):
      temp=input("Enter your pin : ")
      if temp==self.pin:
         amount=int(input("Enter the amount : "))
         self.balance=self.balance+amount
         print("Deposit Sucessfully")
      else:
         print("Invalid pin")   

   def withdraw(self):
      temp=input("Enter your pin : ")
      if temp==self.pin:
         amount=int(input("Enter the amount : "))
         if amount<self.balance:
            self.balance=self.balance-amount
            print("operation sucessfull")
         else:
            print("Insufficient Funds") 
      else:
         print("Invalid Pin : ")  
         
   def check_balance(self):
      temp=input("Enter your pin : ")
      if temp==self.pin:
         print(self.balance)
      else:
         print("invalid pin")