Python Jumpstart by Building 10 Apps Transcripts
Chapter: App 7: Wizard Battle App
Lecture: Concept: Polymorphism
0:00 Let's look at the final core concept
0:02 in this object oriented wizard game called polymorphism.
0:06 Now you can see that we have a list of diverse creatures,
0:09 we have small animals, creatures, dragons, wizards and so on,
0:13 and as you saw on a previous examples
0:15 and you can see in the note on the left here,
0:17 all of these objects all of these classes, small animal, dragon and wizard,
0:20 all derive from creature.
0:23 Below we have a wizard named Gandolf.
0:26 and if he is going to go on some kind of a rampage
0:29 and just start attacking all the creatures
0:30 he would say for c in creatures wizard.attack c,
0:33 now when we write that attack method, we don't care or usually want to know,
0:38 it's usually a negative thing to actually know whether it's a dragon
0:41 a small animal or just a creature
0:44 because we can leverage the fact that all of these derived from creature
0:48 we can just work with the common functionality,
0:51 the fields and the methods on the creature class and it doesn't matter
0:55 what type of derived object we pass, it's a small animal, a dragon,
1:01 we can still fight it just the same, we don't have to rewrite our code,
1:03 and that's fantastic, that lets us as we evolve our application
1:07 create more specialization other types of objects,
1:10 later in the game we want to add some kind of like water monster
1:13 to attack the wizard when he is out in the ocean or something
1:17 as long as that thing derives from creature,
1:20 we potentially don't have to rewrite the code
1:22 that handles wizard's battling water monsters
1:25 it's just using this base class.
1:27 So that's a really powerful feature,
1:29 one other concept closely related to this is something called duck typing,
1:32 in statically typed compiled languages like CSharp, Java, C++ and so on,
1:38 you absolutely must have these objects derived from creature
1:43 or trying to pass them to the attack method
1:46 which assumes it takes a creature literally not compile.
1:49 In Python it's not like that, Python uses something called duck typing
1:55 and as long as the shape of the pieces of the creature class
1:59 that the attack method assumes are there, get defensive roll, name,
2:04 as long as the types you pass match that,
2:07 you technically can use it here, and that is called duck typing,
2:09 it's like if it acts like a creature, if it looks like a creature, it is a creature,
2:13 but I still encourage you to create these object hierarchies
2:16 as it helps reduce code duplication, it helps with maintenance
2:18 and it's generally just the right thing to do.