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The object model in Python is really very powerful and well-designed.

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And Python does support inheritance and polymorphism.

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So let's take a look at an example of how we do inheritance and polymorphism in Python.

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First, we'll make a working copy of oop2.py, and we'll open our working copy, and

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here we have a number of classes, and you'll see we have these animals:

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Dog, Person and Duck. And each of these inherits AnimalActions.

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So AnimalActions has the code in it.

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It has these four methods:

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quack, feathers, bark and fur. And you will notice that each of these methods is

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defined on one line.

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So because each of these methods has just one line of code, you can do it all on one line.

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You have the def keyword, and then you have the name of the method and then the code.

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In this case, it's return self.strings 'quack'.

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This notation here is because strings is a dictionary, and we'll get into that

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later on in the course when we talk about data types. But these strings,

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self.strings, are actually defined in the classes that inherit AnimalActions,

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and so this is an example of inheritance.

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This is also an example of data abstraction, because each of these classes

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has different data.

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So here we have the duck, and it has these four strings in it:

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quack, feathers, bark and fur. And the duck says quack. The duck has gray

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and white feathers. The duck cannot bark. The duck has no fur. And then we

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have a Person, which also inherits AnimalActions, and the Person has quack,

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feathers, bark and fur.

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But for quack, instead of saying quack, the person imitates a duck.

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The person takes a feather from the ground and shows it for feathers.

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For bark, the persons says woof.

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For fur, the person puts on a fur coat, and then we have dog, which also has

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quack, feathers, bark and fur, and does dog-like things with these.

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So this allows us to abstract all of this data, and to use it in exactly the same

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way in each of these classes.

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Because each of these classes inherits AnimalActions, these methods become

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available in each of these other classes.

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So when I create a duck object, here we have donald = Duck,

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that duck object will have these dictionary strings, Quaaaaak!

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The duck has gray and white feathers, and it will also have these action methods:

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quack, feathers, bark and fur.

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And so I can call duck.quack and I can call duck.feathers.

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The beauty of this is that I can also define a Person, john, and I can call

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in_the_forest, where it's expecting a duck, I can call it with john.

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And so here we have an iterator. We are calling for o in ( donald, john, fido),

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so o will be sequentially don and john and fido.

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john is a person; john is not a duck.

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But in_the_forest(o) calls in the forest with john and in_the_forest expects a

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duck object, so it calls duck.quack and duck.feathers.

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Well, john implements - because john is a person, a person inherits AnimalActions,

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and it implements quack and feathers.

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So this is called polymorphism.

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And let's see how this works.

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Remember, we are going to be calling in the doghouse and in the forest for each

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of these three objects:

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donald, john and fido.

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A Duck, a Person and a Dog.

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First, we'll call in the forest for each of them, and then we'll call in the

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doghouse for each of them.

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So I am going to run this.

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And we'll take a look at the results.

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In the forest, we have Quaaaak!

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And the duck has gray and white feathers.

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So we are calling Quaaaak!

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and feathers for each of these.

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We are calling Quaaaak!

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and feathers also for the person, and it says the person imitates a duck, and

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the person takes the feather from the ground and shows it, and also for the dog,

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and then in the doghouse, the duck cannot bark, the duck has not fur, the person says woof!

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the person puts on a fur coat and then for the dog Arf!

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and the dog has white fur with black spots.

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So this is an example of polymorphism and inheritance in Python.

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Now real quick, I want to also show you this example that's been rewritten as a Model-View-Controller.

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Model-View-Controller is a very common pattern in object-oriented programming,

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and I just want to show you that we can do exactly the same thing and actually

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separate it out a little bit further.

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In this case, we are not bothering to define the data for that which doesn't

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apply for each of these.

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So the dog doesn't quack,

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so I am not having a string for dog.

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So this is the modeling, and we have the model for the duck and the person and

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the dog, and each of these inherits AnimalAction. And in this context, we don't

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really care about the implementation of AnimalActions, because all that matters

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is that we are modeling each of these types of objects.

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The view is the implementation of how do we view each of these things?

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So we have these four methods:

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bark, fur, quack and feathers. And they each call doAction with the word bark,

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fur, quack and feathers.

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And then doAction is a local method, and you will notice it has this underscore.

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That doesn't make it special in Python, but it does tell the person who is

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reading it that this is something that's just going to be called internally.

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You are not going to want to call this on the object.

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You are just going to want to call it from inside of the object, or inside of the class.

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So this gets called from each of these methods. And if the action is not found in

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the strings, then it has a default that it does, where it says, this animal name

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has no action. And so that allows us to model these, and to actually expand them,

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and define more actions, and to not have to worry about doing a whole lot of

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extra modifications to the parent class. And then the controller is, of course,

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how we call all of this stuff, which is pretty much the same.

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So this does exactly the same thing. If I go ahead and run this, we'll see that

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our result is exactly the same, but what we have here is a refined version of the

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same thing using a model, view and controller pattern.

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It's a contrived example, but this is commonly how we can do object-oriented

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programming in Python 3.