Output:
Welcome to Python programming.

A variable prefixed with double underscore becomes private in nature. These variables can be accessed only within the class.

The Variables which are defined inside the class is public by default. These variables can be accessed anywhere in the program using dot operator.

When we declare a class variable within the class, methods must be prefixed by the class name and dot operator.

Python class function or method is very similar to ordinary function with a small difference that, the class method must have the first argument named as self.

Any class member i.e. class variable or method (function) can be accessed by using object with a dot (.) operator.

(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

Constructor -( - - init - - ( ))
Destructor -(- - del - - ( ))

Python class function or method is very similar to ordinary function with a small difference. The class method must have the first argument  named as self.

(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