class Sample:
def_init_(self, n1, n2):
self.n1 = n1
self._n2 = n2
def display (self):
print ("class variable 1 =", self.n1)
print ("class variable 2 =", self._n2)
S = Sample (12, 14)
S. display( )
Print ("value 1 = ", S.n1)
print("value 2 =", S._n2)
Output
class variable 1 = 12
class variable 2 = 14
value 1 = 12
Traceback (most recent call last):
File "D:/Python/class-Test-04.py", line 12, in <module>
print(value.2 =", S._n2)
Attribute Error: 'Sample' object has no attribute '_n2'

class sample:
num = 0
def_init_(self, var):
Sample. num +=1
self.var = var
print ("The value is =", var)
print(" The count of objects created = ", Sample.num)
S1 = Sample (15)
S2 = Sample (35)
S3 = Sample (45)
Output:
The object value is = 15
The count of object created = 1
The object value is = 35.
The count of object created = 2
The object value is = 45.
The count of object created = 3 

Output:
value of x = 10
value of Y = 16
value o f x and y = 30

1. It denotes class name
2. x, y is a class variables of the class
3. S is an object created to access the members of the class

1. - y
2. - sample 0
3. - s.x
4. - s. y
5. - s. x + s. y

Program to illustrate about the _del_( ) method
class Sample:
num=()
def _init_(self, var):
Sample.num+= 1
self.var=var
print("The object value is = ", var)
print("The value of class variable is = ", Sample.num)
def _del_(self):
Sample.num-=1
print("Object with value %d is exit from the scope"%self.var)
S1=Sample(15)
S2=Sample(35)
S3=Sample(45)

class Sample:
def _init_(self, n1, n2):
self.n1=n1
self._n2=n2
def display(self):
print("Class variable 1 = ", self.n1)
print("Class variable 2 = ", self._n2)
S=Sample(12,14)
S.display()
print("Value 1 = ", S.n1)
print("Value 2 = ". S._n2)
Reason: The print statements defined within class will successfully display the values of n1 and n2, even though the class variable n2 is private because, in this case, n2 is called by a method defined inside the class. But, when we try to access the value of n2 from outside the class Python throws an error because, private variable cannot be accessed from outside the class.

Output:
The object value is = 15
The count of object created = 1
The object value is = 35
The count of object created = 2
The object value is = 45
The count of object created = 3

(i) The above class "Sample': has only a constructor with one argument named as num. When the constructor gets executed, first the print statement, prints the "Constructor of class Sample ... " then, the passing value to the constructor is assigned to self.num and finally it prints the value passed along with the given string.
(ii) The above constructor gets executed automatically, when an object S is created with actual parameter 10. Thus, the Python displays the following output.
(iii) Constructor of class Sample ...
The value is: 10
Class variable defined within constructor keep count of number of objects created with the class.

class Student:
mark1, mark2, mark3 = 45, 91, 71
#class variable
​​​​​#class method
def process(self):
sum = Student.mark1 + Student.mark2 + Student.mark3
avg = sum/3
print("Total Marks = ", sum)
print("Average Marks = ", avg)
return
S=Student()
S.process()
Output:
Total marks = 207
Average Marks = 69.0

(i) 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.
(ii) No need to pass a value for this argument when we call the method. Python provides its value automatically.
(iii) Even if a method takes no arguments, it should be defined with the first argument called self.
(iv) If a method is defined to accept only one argument it will take it as two arguments ie. self and the defined argument.

(i) Object is a collection of data and function that act on those data. Class is a template for the object
(ii) According to the concept of Object Oriented Programming, objects are also called as instances of a class or class variable.
(iii) In Python, everything is an object. For example, all integer variables that we use in our program is an object of class into Similarly all string variables are also object of class string.