c3.py

class Student:
    def __init__(self,name,rollno):
        self.name=name
        self.__rollno=rollno
    def __repr__(self):
        return "{},{}".format(self.name,self.rollno)

s=Student("Karthi",12)

print (s.name)
#Unable to access attributes having leading double underscore.
print (s.__rollno)#Output:AttributeError: 'Student' object has no attribute '__rollno'
#Name Mangling - have to use class extension with variable name
print (s._Student__rollno)#Output: 12