Python Polymorphism
The word "polymorphism" means "many forms", and in programming it refers to methods/functions/operators with the same name that can be executed on many objects or classes.
Function Polymorphism
An example of a Python function that can be used on different objects is the
len() function.
String
For strings len() returns the number of characters:
Tuple
For tuples len() returns the number of items
in the tuple:
Dictionary
For dictionaries len() returns the number of key/value pairs
in the dictionary:
Example
thisdict = {
"brand": "Ford",
"model": "Mustang",
"year": 1964
}
print(len(thisdict))
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Class Polymorphism
Polymorphism is often used in Class methods, where we can have multiple classes with the same method name.
For example, say we have three classes: Car,
Boat, and Plane, and they all have
a method called move():
Example
Different classes with the same method:
class Car:
def __init__(self, brand, model):
self.brand = brand
self.model = model
def move(self):
print("Drive!")
class Boat:
def __init__(self, brand, model):
self.brand = brand
self.model = model
def move(self):
print("Sail!")
class Plane:
def __init__(self, brand, model):
self.brand = brand
self.model = model
def move(self):
print("Fly!")
car1 = Car("Ford", "Mustang") #Create a Car object
boat1 = Boat("Ibiza", "Touring 20") #Create a Boat object
plane1 = Plane("Boeing", "747") #Create a Plane object
for x in (car1, boat1, plane1):
x.move()
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Look at the for loop at the end. Because of polymorphism we can execute the same method for all three classes.
Inheritance Class Polymorphism
What about classes with child classes with the same name? Can we use polymorphism there?
Yes. If we use the example above and make a parent class called
Vehicle, and make Car,
Boat, Plane
child classes of Vehicle, the child classes
inherits the Vehicle methods, but can override
them:
Example
Create a class called Vehicle and make Car,
Boat, Plane
child classes of
Vehicle:
class Vehicle:
def __init__(self, brand, model):
self.brand = brand
self.model = model
def move(self):
print("Move!")
class
Car(Vehicle):
pass
class Boat(Vehicle):
def
move(self):
print("Sail!")
class
Plane(Vehicle):
def move(self):
print("Fly!")
car1 = Car("Ford", "Mustang") #Create a Car object
boat1 = Boat("Ibiza", "Touring 20") #Create a Boat object
plane1 =
Plane("Boeing", "747") #Create a Plane object
for x in (car1, boat1,
plane1):
print(x.brand)
print(x.model)
x.move()
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Child classes inherits the properties and methods from the parent class.
In the example above you can see that the Car class is empty, but
it inherits brand,
model, and move() from
Vehicle.
The Boat and Plane classes also
inherit brand, model,
and move() from Vehicle, but they both override the
move() method.
Because of polymorphism we can execute the same method for all classes.
