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In designing objects in information sytems, determining relationships between objects is a skill which a designer or analyst must master. One common relationship type is the Generalization/Specification type. The type defines a hierarchy which consists of a superclass and multiple subclasses. A subclass inherits everything from its superclass, which is referred to as inheritance in the object-orientation methodology and object-oriented programming. By inheritance, the superclass’s attributes will not repeat in any of its subclasses. When a new object of subclass is created, no extra object of the superclass is needed.

The following Python code shows you how to implement two classes: Person and Student. Student inherits all the attributes, fname and lname, as well as the methods, initializer and toString, from Person. In addition, Student has its own attribute: year.


Source code

#Define the Person class
class Person:
  def __init__(self, fname, lname):
    self.firstname = fname
    self.lastname = lname

  def printname(self):
    print(self.__class__.__name__,":", self.firstname, self.lastname)

#Use the Person class to create an object, and then execute the printname method:
x = Person("John", "Doe")

#Define a Child class of Person
class Student(Person):
  def __init__(self, fname, lname, year):
    super().__init__(fname, lname)
    self.year = year

  def printname(self):

#Create a new Student object
x = Student("Mike", "Olsen", 2019)
#Create a new Student object
x = Student("Joker", "Lee", 2018)
#Create a new Student object
x = Student("Swan", "Alter", 2017)
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