Polymorphism

While inheritance is the most unique trait of object-oriented languages, polymorphism is probably the most powerful. It also is not particularly unique to class-based languages. Polymorphism is the ability of a variable, function or object to take on multiple forms.

• "poly" = "many"
• "morph" = "form"

For example, classes in the same hierarchical tree may have methods with the same name and signature but different implementations. Here's a simple example:

class Creature:
    def move(self) -> None:
        print("the creature moves")


class Dragon(Creature):
    def move(self) -> None:
        print("the dragon flies")


class Kraken(Creature):
    def move(self) -> None:
        print("the kraken swims")


creatures: list[Creature] = [Creature(), Dragon(), Kraken()]
for creature in creatures:
    creature.move()
# prints:
# the creature moves
# the dragon flies
# the kraken swims

Because all three classes have a .move() method, we can shove the objects into a single list, and call the same method on each of them, even though the implementation (method body) is different.