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In object-oriented programming, inheritance is when one class inherits the

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properties of another class.

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The class that is being inherited from is often called a base class or a parent class.

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Let's take a look at how this is done in Python.

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We'll start by making a working copy of classes.py, classes-working.py, and

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we'll open our working copy.

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You notice that we have this Duck class here.

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We're going to create another class.

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We'll call this one Animal.

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So the Animal class will have methods in it that will be inherited by the Duck

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class and perhaps other animals as well.

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We'll start by saying that an animal makes a sound, so we'll call talk and that

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will print 'I have something to say!', and say that the animal moves around.

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We'll call that walk, print. 'Hey!

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I' 'm walkin'' here!' And then an animal is covered with something, usually fur or

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feathers or something. We'll call that clothes.

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'I have nice clothes'. [00:01:22.02

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All right. So there is our animal.

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Now, Duck can inherit all of these methods from Animal, in fact all of its

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attributes, by simply saying Animal here.

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Putting in a parenthesis in the definition of Duck.

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Now, Duck is said to be, is an animal. Duck is a animal.

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Object-oriented speak for saying that the Duck inherits the properties of Animal.

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So Duck will continue to work the same way that it did before.

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If we save this and we run it, we don't really see any difference in how it works.

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Except that now it has access to these other properties.

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I can say donald.clothes and save that and run it.

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And we see donald says he has nice clothes.

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You'll notice that walk printed "Walks like a duck."

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It did not print "Hey! I'm walkin' here!"

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That's because walk in Duck overrides walk in Animal.

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The way that works is that Duck inherits Animal and then Duck defines a

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method called walk, so it uses this one instead of the one in its parent.

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If we wanted to say incorporate the one from its parent, we can do that with the

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super function. This is a built-in function which accesses the parent class and

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just say, super().walk() like that, and now donald will do both.

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Save that and run it, and he says, "Hey! Im walkin here!"

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And he says, "Walks like a duck."

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So this is how you can access the class in the parent, even though you're

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overriding it in the class that inherits from the parent.

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So what makes this useful is that now we've defined an animal base class and now

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if we want to have another animal, it's very easy for us to do that.

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We can say class Dog and it inherits from Animal, and that's really all that we need to define.

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We can just say pass here and we can say fido = Dog(), and fido.walk(), and

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we have a working dog.

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Save that and run it.

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And there we have, "Hey! I'm walkin' here!"

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And that's from fido.

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So obviously a dog, instead of having clothes, he is got fur. So we can say, def

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clothes, print, 'I have brown and white fur'.

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And then down here if we say fido.clothes(), save that and run it, and it says,

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"I have brown and white fur."

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But what we've done is we've created a base class that perhaps has all the

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properties that are going to be common to the classes that we're creating and

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then we simply inherit that and that makes our code very reusable.

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You'll see this technique used a lot.

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In fact, in an object-oriented language like Python, virtually all of the

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classes at some level are inheriting form other classes.

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You have two classes like the tuple and the list and they do a lot of

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common similar things.

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In fact, strings do as well.

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And so those are all inheriting from some common classes and simply building

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upon that and overwriting some methods and implementing some and not

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implementing others.

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And that allows them to reuse a lot of code and it also allows them to operate

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in a lot of the same contexts as each other.

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So this is inheritance and this is how you do inheritance in Python.