OOP - cont'

Inheritance

# define a superclass
class super_class:
    # attributes and method definition
    pass

# inheritance
class sub_class(super_class):
    # attributes and method of super_class
    # attributes and method of sub_class
    pass

class Animal:
    # attribute and method of the parent class
    name = "" # for educational purposes !!!

    def eat(self):
        print("I can eat")

class Dog(Animal):
    # attribute and method of the child class
    def display(self):
        print("My name is ", self.name)

dog = Dog() # instance of the class Dog
dog.name = 5 # attribute of the parent class
dog.eat()  # method of the parent class
dog.display() # method of the subclass (child) class

I can eat
My name is  5

issubclass()

issubclass(subclass,object)

issubclass(Dog, Animal)

True

issubclass(Animal,Dog)

False

issubclass(Dog, (Animal,int))

True

Overriding

class Animal:

    # attributes and method of the parent class
    name = ""

    def eat(self):
        print("I can eat")

    def sleep(self):
        print("I can sleep")

# inherit from Animal
class Dog(Animal):
    def eat(self):
        '''override eat() method'''
        print("I like to eat bones")

animal = Animal()
animal.eat()
animal.sleep()
dog = Dog()
dog.eat()
dog.sleep()

I can eat
I can sleep
I like to eat bones
I can sleep

super()

class Animal:

    # attributes and method of the parent class
    name = ""

    def eat(self):
        print("I can eat")

    def sleep(self):
        print("I can sleep")

# inherit from Animal
class Dog(Animal):
    def eat(self):
        '''override eat() method'''
        super().eat()
        print("I like to eat bones")

animal = Animal()
animal.eat()
animal.sleep()
print('-' * 10)
dog = Dog()
dog.eat()
dog.sleep()

I can eat
I can sleep
----------
I can eat
I like to eat bones
I can sleep

print(type(animal))
isinstance(animal, Animal)

<class '__main__.Animal'>

True

isinstance(5, (float,int))

True

class Person:
  def __init__(self, fname = 'John', lname = 'Dow'):
    self.firstname = fname
    self.lastname = lname

  def printname(self):
    print(self.firstname, self.lastname)

class Student(Person):
  pass

x = Person()
x.printname()
y = Student() # inhereted init from person
y.printname()

John Dow
John Dow

class Person:
  def __init__(self, fname = 'John', lname = 'Dow'):
    self.firstname = fname
    self.lastname = lname

  def printname(self):
    print(self.firstname, self.lastname)

class Student(Person):
  def __init__(self, fname = 'John', lname = 'Jones', graduationyear = 2019):
    super().__init__(fname, lname)
    self.graduationyear = graduationyear

  def printname(self):
     print(self.firstname, self.lastname, self.graduationyear)

  def welcome(self):
    print("Welcome", self.firstname, self.lastname, "to the class of", self.graduationyear)

x = Person()
x.printname()
y = Student() # inhereted init from person
y.printname()
y.welcome()

John Dow
John Jones 2019
Welcome John Jones to the class of 2019

Overloading

class Point:
    def __init__(self, x=0, y=0):
        self.x = x
        self.y = y

    def __str__(self):
        return f"({self.x}, {self.y})"

    def __len__(self):
       return 1

    def __add__(self, other):
        '''override + operator
        input: other - another Point instance
        output: Point instance
        '''
        return Point(self.x + other.x, self.y + other.y)

p1 = Point(1, 2)
p2 = Point(2, 3)
p3 = p1 + p2
print(p1)
print(p3)
print(isinstance(p1,Point))
isinstance(p1+p2,Point)

(1, 2)
(3, 5)
True

True

isinstance(Point(),Point)
# Point() - instance
# Point - class

True

print(Point)
print(Point())

<class '__main__.Point'>
(0, 0)

lst = [Point(),Point(1,2)]
for x in lst:
    print(x)

(0, 0)
(1, 2)

points = []
lst2 = [Point,Point]
for x in lst2:
    points.append(x())

[<__main__.Point object at 0x7d0b734e81f0>, <__main__.Point object at 0x7d0b734eab90>]

lst3 = [Point,Point()]
print(lst3)

[<class '__main__.Point'>, <__main__.Point object at 0x7d0ba43ffd90>]

len(p1)

1