WEBVTT 0 00:00.050 --> 00:06.260 Let's talk about another feature of Object-Oriented Programming that's really, really handy. 1 00:06.260 --> 00:09.590 And it's something that we call Class Inheritance. 2 00:09.740 --> 00:11.090 How does this work? 3 00:11.090 --> 00:17.750 Well, let's say that you code up a Robot Chef and you give it a bunch of functionality like you tell 4 00:17.750 --> 00:21.320 it how to bake, how to stir, how to measure, 5 00:21.320 --> 00:27.170 and then at some point, you decide actually, you know, in my restaurant, I also need a Pastry Chef. 6 00:27.170 --> 00:33.280 Now, this pastry chef will need to know some of the things that a chef knows how to do, but it also 7 00:33.280 --> 00:34.810 needs something extra. 8 00:34.810 --> 00:38.950 So you don't want to create this pastry chef entirely from scratch. 9 00:38.950 --> 00:44.740 Instead, what you want to do is you want to be able to take the methods you already defined for the 10 00:44.740 --> 00:47.470 Chef class and then just add to it. 11 00:47.470 --> 00:53.470 Add a few other relevant methods like how to knead dough, or how to whisk some eggs. 12 00:53.470 --> 01:02.500 So this process of inheriting behavior and appearance from an existing class is known as Class Inheritance. 13 01:02.620 --> 01:07.360 When we're talking about class inheritance, you can inherit both appearance, 14 01:07.360 --> 01:14.380 so attributes, like for example, if you inherited the same eyes as your mother, or if you inherited 15 01:14.380 --> 01:19.300 the same nose as your grandfather, but you can also inherit behavior. 16 01:19.300 --> 01:24.970 So maybe you chop tomatoes in the same way that your dad chops tomatoes. 17 01:24.970 --> 01:30.550 And if you believe my mother, I'm lazy in the same way that my dad is lazy. 18 01:30.550 --> 01:35.710 So not only can win inherit appearance, but we can also inherit behavior. 19 01:35.740 --> 01:39.850 Now, how does inheritance actually work in terms of the code? 20 01:39.880 --> 01:43.450 Well, we can define a class, let's call it Fish, 21 01:43.450 --> 01:46.280 and it has an initializer. 22 01:46.310 --> 01:54.350 Now, in order to get this Fish class to inherit from another class, all we have to do is to add a 23 01:54.350 --> 02:00.200 set of parentheses after the name of the class, and then provide the class that we want to inherit 24 02:00.200 --> 02:00.800 from. 25 02:00.830 --> 02:05.030 So in this case, our Fish is inheriting from the Animal class. 26 02:05.030 --> 02:12.890 And then in order to get hold of everything that an animal has and is so its attributes and methods, 27 02:12.890 --> 02:15.320 all we have to do is inside the __init__(), 28 02:15.320 --> 02:21.680 add this super().__init__(), and this super refers to the superclass. 29 02:21.680 --> 02:28.250 So basically initialize everything that the superclass can do in our Fish class. 30 02:28.250 --> 02:31.820 Let's take a look at this in terms of real code. 31 02:31.850 --> 02:34.970 First I'm going to create an Animal class, 32 02:34.970 --> 02:42.310 and this Animal class is going to have an initializer where we're able to define some attributes. 33 02:42.310 --> 02:42.580 Right? 34 02:42.580 --> 02:47.050 So let's say that all animals have two eyes, 35 02:47.050 --> 02:49.990 so num_eyes = 2. 36 02:50.080 --> 02:55.900 Now at the same time, I'm also going to define a method associated with this Animal class. 37 02:55.900 --> 02:59.170 Let's say that all animals know how to breathe. 38 02:59.170 --> 03:03.390 So inside this breathe() method, I'm going to keep it quite simple, 39 03:03.390 --> 03:05.970 I'm just going to say, ("Inhale, exhale"). 40 03:06.690 --> 03:08.790 So that's breathing done. 41 03:08.790 --> 03:13.050 Now later on I decide to define a Fish class, 42 03:13.140 --> 03:16.860 and this Fish class probably also knows how to do certain things. 43 03:16.860 --> 03:20.670 So for example maybe it knows how to swim, right? 44 03:22.740 --> 03:23.190 Right 45 03:23.190 --> 03:29.690 now if I create an object from this Fish class, let's say I create an object called nemo that's created 46 03:29.690 --> 03:30.980 from the Fish class, 47 03:30.980 --> 03:34.040 then I can say nemo.swim(). 48 03:34.520 --> 03:39.620 And you can see when I run this code it says that nemo is moving in water. 49 03:39.740 --> 03:47.390 Now what if I wanted this Fish class to inherit everything that the Animal class can do, including 50 03:47.390 --> 03:51.980 the attribute, num_eyes, and also the method breathe()? 51 03:52.010 --> 04:00.650 All I have to do is to add this Animal class after the name of the Fish class inside parentheses, and 52 04:00.650 --> 04:09.230 then I have to add the initializer and inside the initializer, I have to trigger a call to the superclass(), 53 04:09.230 --> 04:11.780 which is in this case the Animal class, 54 04:11.780 --> 04:16.720 and then I'm going to call the initializer like this. 55 04:16.720 --> 04:23.860 So now what these two parts of the code does is it allows anything that's created from my Fish class 56 04:23.860 --> 04:30.340 to inherit all of the attributes and methods from the superclass, which is the Animal class. 57 04:30.340 --> 04:39.580 Now I can get my nemo to start breathing and you can see if I hit Run, then it will also Inhale and 58 04:39.580 --> 04:40.450 exhale. 59 04:40.450 --> 04:48.030 And in addition, if I wanted to print, nemo.num_eyes then you can see this is also going to print 60 04:48.030 --> 04:48.690 too. 61 04:48.720 --> 04:56.550 So now my object that's created from the Fish class now has access to all the attributes and methods 62 04:56.550 --> 05:00.570 from the superclass that inherited from the Animal class. 63 05:00.600 --> 05:08.580 Now what if I wanted to inherit a method so get all the things that it does, for example in the breathe() 64 05:08.580 --> 05:09.180 method, 65 05:09.180 --> 05:12.390 but what if I wanted to modify it a little bit? 66 05:12.390 --> 05:17.760 So for example, a Fish does in fact breathe, but it kind of breathes underwater. 67 05:17.760 --> 05:21.570 So let's say I wanted to define the breathe() function, 68 05:21.570 --> 05:27.420 and I want it to have the same functionality as the superclass which I'm inheriting from. 69 05:27.420 --> 05:30.090 So I want to print, inhale, exhale, 70 05:30.090 --> 05:32.540 but I also want to do something extra. 71 05:32.570 --> 05:38.390 Well in this case we would get hold of the superclass and then call breathe() on it. 72 05:39.470 --> 05:45.020 This means we're going to do everything that the breathe() method from the superclass does. 73 05:45.020 --> 05:46.280 So all of this. 74 05:46.280 --> 05:50.150 But afterwards we're going to do something a little bit more special. 75 05:50.150 --> 05:54.980 So we're going to say, "We're doing this underwater." 76 05:55.010 --> 06:03.310 Now when this line nemo. breathe() gets run, you can see what happens is it will print out Inhale, 77 06:03.310 --> 06:04.090 exhale, 78 06:04.090 --> 06:08.740 and this comes from the superclass's breathe() method here. 79 06:08.740 --> 06:16.090 And then afterwards it will print its own unique twist on breathing, which is, "doing this underwater." 80 06:16.420 --> 06:18.250 By learning about inheritance, 81 06:18.250 --> 06:24.520 what it allows us to do is to take an existing class that we've created, or somebody else has created, 82 06:24.520 --> 06:30.940 and then build on top of it without having to reinvent the wheel and redefine everything that's in that 83 06:30.940 --> 06:31.690 class. 84 06:31.690 --> 06:37.540 So in the next lesson, I'm going to show you how we can inherit from the turtle class, to upgrade 85 06:37.540 --> 06:44.020 the turtle, to be able to do extra things, such as creating a piece of food, or creating a scoreboard 86 06:44.020 --> 06:45.760 For all of that and more, 87 06:45.760 --> 06:47.380 I'll see you on the next lesson.