OOPs Concepts:
==============

Constructor:
============
1) always can define inside the class only.
2) __init__
3) can always define with keyword: "def" like a method.
4) method can be named with any identifier
whereas the constructor can be named with only "__init__".
4) method can be invoked using an object to execute the block of code.
Whereas the constructor can be invoked automatically at the time of object creation. 

#  constructor

class myClass:
    # constructor without parameters
    def __init__(self):
        print("Hi")
        print("Hello")
        print("Good Evening.")

    def method(self):
        print("Good Night.")

mc = myClass()      # Object creation
mc.method()

5) If the constructor with more than one definitions, then the constructor can be overwritten with latest definition.

#  constructor

class myClass:
    # constructor without parameters
    def __init__(self):
        print("Hi")
        print("Hello")
        print("Good Evening.")

    def method(self):
        print("Good Night.")

    def __init__(self):
        print("Hello all. Welcome to Python's OOP Concepts.")

mc = myClass()      # Object creation
mc.method()

================================================
6) Like methods, the constructor can accept parameters.

# Constructor with parameters

class Employee:
    def __init__(self,eid,ename,esal):
        print("The Employee Name = ",ename)
        print("The Employee Id =",eid)
        print("The Employee Salary = ",esal)

emp = Employee(110,"Avinash",150000)

7) The Constructor can always return "None".

===================================
Differences Between Constructor and Method:
===========================================
1) Method can define with any identifier
constructor can always define with "__init__" only.
2) Method can return anything
constructor can return "None"
3) Method can allow to define the business logic of the application
constructor can use to define the definition of data only.

# Constructor Vs Method

class myClass:
    def __init__(self):
        self.a = 100
        self.b = 200
        self.c = 300

    def findBig(self):
        if self.a > self.b and self.a > self.c:
            bigger = self.a
        elif self.b > self.c:
            bigger = self.b
        else:
            bigger = self.c
        return bigger

mc = myClass()
result = mc.findBig()
print("The Biggest number = ",result)

4) Constructor can be invoked automatically at the time of object creation
method need to be invoke using an object of the class.

=============================================

Types of Variables:
===================
three types:
	1) Instance Variables (Object Level Variables)
	2) Static Variables (Class Level Variables)
	3) Method Variables (Method Level Variables/Local Variables)

1) Instance Variables
=====================
The value of the variable can be varied from object to object, these variables are called "Instance Variables".
Instance Variables can de declared in:
	1) Inside the Constructor
	2) Inside the Method
	3) Using an Object of the class

1) Inside the Constructor
=========================
==> to define the instance variables inside the constructor, we can use "self" keyword.

# Instance Variable in Constructor

class Employee:
    def __init__(self):
        # Instance Variables definition
        self.eid = int(input("Enter Empolyee Id:"))
        self.ename = input("Enter Employee Name:")
        self.erole = input("Enter Employee Role:")
        self.esal = int(input("Enter Employee Salary:"))

    def printData(self):
        print("The Employee Details:")
        print("Id = ",self.eid)
        print("Name = ",self.ename)
        print("Role = ",self.erole)
        print("Salaray = ",self.esal)

emp = Employee()
emp1 = Employee()

emp.printData()
emp1.printData()

=============================
2) Inside the Method
====================

# Instance Variables in methods

class Test:
    def __init__(self):
        self.a = 11
        self.b = 21

    def testMethod(self):
        self.c = 31
        self.d = 41

    def printMethod(self):
        print("The Instance Variables are:")
        print(self.a,self.b,self.c,self.d)

t = Test()

t.testMethod()
t.printMethod()

=========================================
Using an Object of the class
=============================

# Instance Variables in methods

class Test:
    def __init__(self):
        self.a = 11
        self.b = 21

    def testMethod(self):
        self.c = 31
        self.d = 41

    def printMethod(self):
        print("The Instance Variables are:")
        print(self.a,self.b,self.c,self.d)

t = Test()

t.testMethod()
t.printMethod()

print(t.__dict__)

t.e = 51

print(t.__dict__)