(i) The variables which are defined inside the class is public by default. These variables can be accessed anywhere in the program using dot operator.
(ii) A variable prefixed with double underscore becomes private in nature. These variables can be accessed only within the class

In the program, class variable num is shared by all three objects of the class Sample. It is initialized to zero and each time an object is created, the num is incremented by 1. Since, the variable shared by all objects, change made to num by one object is reflected in other objects as well

Program to illustrate Constructor:
class Sample:
def _init_(self, num):
print("Constructor of class Sample...")
self.num=num
print("The value is :", num)
S = Sample(10)
Output:
constructor of class Sample..
The value is:10

(i) Object - name = class_name ()
(ll) Object - name = class_member

In Python, a class is defined by using the keyword class. Every class has a unique name followed by a colon (:).
Syntax:
class class_name:
statement_1
statement_2
.................
.................
statement_n

Destructor is also a special method to destroy the objects. In Python,__del__( ) method is used as destructor. It is just opposite to constructor.

(i) "Init" is a special function begin an end with double underscore in Python act as a Constructor .
(ii) Constructor function will automatically executed when an object is created.
General format of __init__ method
                                    (Constructor function)
def __init__ (self, [args........])
<statements>

Output:
>>>
10
line 7, in <module>
print(S._num)
AttributeError: 'Sample' object has no attribute '_num'
>>>

Once a class is created, next to create an object or instance of that class. This process of creating object is called as "Class Instantiation".

(i) Class is the main building block in Python.
(ii) Class is a template for the object.
(iii) Object is a collection of data and function that act on those data.
(iv) Objects are also called as instances of a class.