1. polymorphism Inheritance Base class Derived class

2. recall from last class -polymorphism
r = a rectangle t = a triangle c = a circle txt = some text shapeList=[r,t,c,txt] for shape in shapeList: shape.draw(win)

3. Inheritance
mammal, horse, kangaroo
mammal
horse
kangaroo

4. Inheritance mammal, horse, kangaroo mammal backbone fur mammal horse
4 legs
tail
kangaroo
backbone
fur
pocket
tail
horse
kangaroo

5. Inheritance Inheritance :derive a new class from an existing one
existing class:the parent class, or superclass, or base class
The new class: derived class ,the child class or subclass
the child inherits characteristics of the parent
That is, the child class inherits the methods and data defined by the parent class
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6. is-a relationship
get all the member variables get all the member methods if you want. can add more variables can add or modify methods software reuse is good – already tested, etc.

7. Base class: Animal
class Animal: #base class def __init__(self,name="just an animal",flies=False): self.name=name self.flies=flies def display(self): print(self.name, end="") def talk(self): print("Indistinct animal noises") #This eat method will be used, unchanged, for Duck. def eat(self): print("Eat, eat, eat.")

8. Base class: Animal - constructor
class Animal: #base class
def __init__(self,name="just an animal",flies=False):
self.name=name
self.flies=flies
Has instance data
self.name (a string)
self.flies(boolean, default is False)

9. Base class: Animal – other methods
def display(self): print(self.name, end="") def talk(self): print("Indistinct animal noises") #This eat method will be used, # unchanged, for Duck. def eat(self): print("Eat, eat, eat.")

10. Derived class: Duck
class Duck(Animal): #The derived constructor calls # the base constructor, # then does more def __init__(self, feathers): Animal.__init__(self,"duck") self.flies=True self.feathers=feathers

11. Derived class: Duck - constructor
class Duck(Animal):
#The derived constructor calls
# the base constructor,
# then does more
def __init__(self, feathers):
Animal.__init__(self,"duck")
self.flies=True
self.feathers=feathers
instance data
self.name (from Animal)
self.flies (from Animal)
self.feathers (just for Duck)

12. Derived class: Duck – other methods
#This display does more than the animal display, #but makes use of Animal.display def display(self): print("I am a", end=" ") Animal.display(self) print(" with ",self.feathers, " feathers") #This talk totally overrides the Animal talk def talk(self): print("Quack! Quack!") # Animal has no move method. Only for Ducks. def move(self): print("I swim. I fly. I walk")

13. main
def main(): a=Animal() a.display() print() a.talk() a.eat() d=Duck(1000) d.display() d.talk() d.eat() d.move()

14. class Animal: #base class def __init__(self,name="just an animal",flies=False): self.name=name self.flies=flies def display(self): print(self.name, end="") def talk(self): print("Indistinct animal noises") #This eat method will be used, unchanged, for Duck. def eat(self): print("Eat, eat, eat.")

15. main
def main(): a=Animal() a.display() print() a.talk() a.eat() d=Duck(1000) d.display() d.talk() d.eat() d.move()
just an animal
self.name
False
self.flies a
just an animal
Indistinct animal noises
Eat, eat, eat.

16. class Animal: #base class def __init__(self,name="just an animal",flies=False): self.name=name self.flies=flies def display(self): print(self.name, end="") def talk(self): print("Indistinct animal noises") #This eat method will be used, unchanged, for Duck. def eat(self): print("Eat, eat, eat.")

17. class Duck(Animal): #The derived constructor calls the base constructor, #then does more def __init__(self, feathers): Animal.__init__(self,"duck") self.flies=True self.feathers=feathers #This display does more than the animal display, #but makes use of Animal.display def display(self): print("I am a", end=" ") Animal.display(self) print(" with ",self.feathers, " feathers") #This talk total overrides the Animal talk def talk(self): print("Quack! Quack!") # Animal has no move method. Only for Ducks. def move(self): print("I swim. I fly. I walk")

18. main
just an animal
Indistinct animal noises
Eat, eat, eat.
I am a duck with feathers
Quack! Quack!
I swim. I fly. I walk
def main(): a=Animal() a.display() print() a.talk() a.eat() d=Duck(1000) d.display() d.talk() d.eat() d.move() a
just an animal
self.name
False
self.flies
1000
self.feathers
duck
self.name
False True
self.flies d