WEBVTT 1 00:00:00.370 --> 00:00:02.700 Classes are all about organization. 2 00:00:02.700 --> 00:00:06.280 They're a solid reliable way to break up your monolithic scripts into smaller 3 00:00:06.280 --> 00:00:10.410 chunks so they're easier to understand, easier to reuse, and easier to customize. 4 00:00:10.410 --> 00:00:14.700 You've already seen how we can use super to reuse the code written in a superclass, 5 00:00:14.700 --> 00:00:17.380 but that only gets us part of the way there. 6 00:00:17.380 --> 00:00:18.990 If we continue with our current example, 7 00:00:18.990 --> 00:00:22.860 our Thief class, think of all the things we eventually have to have in there. 8 00:00:22.860 --> 00:00:25.870 Thieves can pick pocket, hide in the shadows, throw a few nasty daggers, 9 00:00:25.870 --> 00:00:29.050 and dodge attacks better than some strong but slow warrior. 10 00:00:29.050 --> 00:00:31.790 We don't want to implement all of that on our Thief class. 11 00:00:31.790 --> 00:00:34.080 Especially when other classes like maybe an assassin or 12 00:00:34.080 --> 00:00:37.000 a ninja would meet some of those abilities too. 13 00:00:37.000 --> 00:00:38.420 Let's get back to workspaces and 14 00:00:38.420 --> 00:00:41.150 look at extending several classes to make one awesome one. 15 00:00:42.870 --> 00:00:46.010 Alright, things have changed a little bit so you'll want to be sure and 16 00:00:46.010 --> 00:00:49.600 relaunch the work space if you're following along in workspaces. 17 00:00:49.600 --> 00:00:53.670 Now, I've prepared a couple of classes and modules already. 18 00:00:53.670 --> 00:00:56.430 Here, there's this attributes.py module and 19 00:00:56.430 --> 00:00:58.460 you can see we're inside the RPG directory. 20 00:00:59.620 --> 00:01:02.800 And inside here, we have an Agile attribute and 21 00:01:02.800 --> 00:01:04.510 we have a Sneaky one as well. 22 00:01:04.510 --> 00:01:08.370 We'll use both of these, but say we're making a gymnast, they might be agile but 23 00:01:08.370 --> 00:01:10.970 they wouldn't necessarily be sneaky. 24 00:01:10.970 --> 00:01:14.495 I've also refactored the Thief class out into its own module called 25 00:01:14.495 --> 00:01:16.950 thieves.py, wait a minute. 26 00:01:16.950 --> 00:01:19.290 Refactored, what kind of word is that? 27 00:01:19.290 --> 00:01:23.820 Well, refactoring is a common programming concept that sometimes is as easy as 28 00:01:23.820 --> 00:01:27.260 cutting and pasting some code from one place to another. 29 00:01:27.260 --> 00:01:29.485 Sometimes it's more complicated than that. 30 00:01:29.485 --> 00:01:33.365 Ultimately though, it's just the tech jargon word for rearranging code into 31 00:01:33.365 --> 00:01:37.885 a more logical state through renaming things, moving code between files, or 32 00:01:37.885 --> 00:01:42.265 deleting or combining code where too much optimization was done. 33 00:01:42.265 --> 00:01:45.955 So our thief character is still pretty similar to how it was before. 34 00:01:45.955 --> 00:01:50.720 Thief inherits from Character, but you notice we're not setting sneaky or agile. 35 00:01:50.720 --> 00:01:53.380 We're gonna handle those inside these attributes. 36 00:01:54.850 --> 00:01:56.310 So let's go ahead and do that. 37 00:01:56.310 --> 00:02:00.330 I want this to be a sneaky, agile character, and 38 00:02:00.330 --> 00:02:01.960 of course it should still be a character. 39 00:02:01.960 --> 00:02:08.870 So let's say, from attributes import Agile and Sneaky. 40 00:02:08.870 --> 00:02:12.220 And now I need to use them in the definition of my class, 41 00:02:12.220 --> 00:02:15.500 now the order that you add items into the inheritance chain of your class, 42 00:02:15.500 --> 00:02:20.940 this list of classes here that your class extends, that order matters. 43 00:02:20.940 --> 00:02:24.450 It matters because of things like super and how Python figures out which super 44 00:02:24.450 --> 00:02:28.800 classes methods to call when two of them have methods with the same name. 45 00:02:28.800 --> 00:02:32.410 This the called the method resolution order or MRO. 46 00:02:32.410 --> 00:02:33.950 And it can cause a lot of headaches. 47 00:02:33.950 --> 00:02:38.800 But Python has gotten better and better at making things just work for you. 48 00:02:39.930 --> 00:02:42.980 Well, let's look at our sneaky and agile classes. 49 00:02:42.980 --> 00:02:46.680 Now, they both have an init inside of them. 50 00:02:46.680 --> 00:02:52.080 And in both of them, the __init__ calls super, and it passes on args and kwargs. 51 00:02:52.080 --> 00:02:53.290 So, that's good. 52 00:02:53.290 --> 00:02:56.640 And they don't have any other methods where the names conflict. 53 00:02:56.640 --> 00:02:59.640 So, they should be fine to use in either order. 54 00:02:59.640 --> 00:03:01.830 You know what? I'm kinda tired to thinking about this. 55 00:03:01.830 --> 00:03:03.460 I'm just gonna use them as if they're modifiers. 56 00:03:03.460 --> 00:03:04.670 I'm gonna make a sentence, right? 57 00:03:04.670 --> 00:03:08.490 So Character that is Agile and Sneaky. 58 00:03:08.490 --> 00:03:11.740 I'm also getting kind of tired of testing this down in the shell constantly, 59 00:03:11.740 --> 00:03:13.499 like having to import and making things. 60 00:03:13.499 --> 00:03:17.175 So let's make a new file that we will call play.py, and 61 00:03:17.175 --> 00:03:22.401 inside of here we'll import our Thief class from thieves import Thief, and 62 00:03:22.401 --> 00:03:27.970 then we'll say that kenneth is equal to a Thief(), and we give it the name Kenneth. 63 00:03:29.610 --> 00:03:35.065 And then let’s print kenneth.sneaky, 64 00:03:35.065 --> 00:03:40.150 kenneth.agile, let’s just print those for right now. 65 00:03:40.150 --> 00:03:42.630 That covers two of our special attributes, right? 66 00:03:42.630 --> 00:03:47.910 Maybe we will do a print kenneth.hide when the light level is 8. 67 00:03:49.723 --> 00:03:53.147 All right, I think that's pretty good, and you know what, 68 00:03:53.147 --> 00:03:55.870 let's do, here, let's say sneaky=False. 69 00:03:55.870 --> 00:03:59.610 All right, that covers a lot of our stuff, 70 00:03:59.610 --> 00:04:03.560 now feel free to change these attributes, change the names, 71 00:04:03.560 --> 00:04:07.940 all that kind of stuff, make this your own code, you don't have to copy me exactly. 72 00:04:07.940 --> 00:04:12.560 All right, so now let's try Python play. 73 00:04:12.560 --> 00:04:15.680 And we get False for sneaky, because we set sneaky to False. 74 00:04:15.680 --> 00:04:16.250 We get True for 75 00:04:16.250 --> 00:04:21.320 agile because we didn't change that, and I failed to hide because I'm not sneaky. 76 00:04:21.320 --> 00:04:22.080 All right. 77 00:04:22.080 --> 00:04:25.350 But let's think about design for a minute, right? 78 00:04:26.940 --> 00:04:30.248 Sometimes if you run this code, depending on the version of Python that you're on, 79 00:04:30.248 --> 00:04:30.955 this might fail. 80 00:04:30.955 --> 00:04:35.980 You might get an error that there's no attribute Agile or no attribute Sneaky. 81 00:04:35.980 --> 00:04:41.343 And even though we're using super on all of these, sometimes the keys and 82 00:04:41.343 --> 00:04:46.101 values don't always get passed up to where they need to be because 83 00:04:46.101 --> 00:04:51.230 the MRO falls down and Python fails to put things where they need to go. 84 00:04:51.230 --> 00:04:53.978 So, okay, as part of that, 85 00:04:53.978 --> 00:04:59.490 we could add a super into the init of our character class. 86 00:05:00.540 --> 00:05:05.570 And then everything should work in all versions of python no matter where we are, 87 00:05:05.570 --> 00:05:08.510 right, and no matter how the inheritance chain is set up. 88 00:05:08.510 --> 00:05:13.030 But, usually you want something that's more concrete as a class, 89 00:05:13.030 --> 00:05:15.310 a class where things just stop, right? 90 00:05:15.310 --> 00:05:19.850 It's the concrete, and right now I would think that our Character class is 91 00:05:19.850 --> 00:05:23.590 the class that we want that, and we kind of have designed that, because our 92 00:05:23.590 --> 00:05:28.110 Character class doesn't have a super in it, since it doesn't super anything, 93 00:05:28.110 --> 00:05:31.480 it's expecting to be the final class that gets initialized. 94 00:05:31.480 --> 00:05:32.910 Well that's cool, we can do that. 95 00:05:32.910 --> 00:05:36.190 If it wants to be the final class, let's make it the final class. 96 00:05:36.190 --> 00:05:41.880 So we'll put Character out here, and then we'll, 97 00:05:43.640 --> 00:05:48.740 over this way and delete Character off of there. 98 00:05:48.740 --> 00:05:53.190 And that reads better too, right, our thief is an agile sneaky character. 99 00:05:53.190 --> 00:05:54.690 Okay, so let's see if this is still working. 100 00:05:56.910 --> 00:06:01.770 And now we've got an error, we didn't get this error before, but now we get one. 101 00:06:01.770 --> 00:06:08.421 And this time it says that init is missing a required positional argument name. 102 00:06:08.421 --> 00:06:11.630 Okay, now, I know that we provided a name value, right? 103 00:06:11.630 --> 00:06:13.860 We provided name right here. 104 00:06:13.860 --> 00:06:17.196 But, this is what I was talking about with the super calls, 105 00:06:17.196 --> 00:06:21.933 from the time it goes to this super calls, it's a lot of this positional argument and 106 00:06:21.933 --> 00:06:24.290 doesn't put name or this arg. 107 00:06:24.290 --> 00:06:28.530 It doesn't put this arg as the first argument that provided. 108 00:06:28.530 --> 00:06:31.530 So, we have to make another design decision. 109 00:06:31.530 --> 00:06:36.006 Now, we could go into our attributes and we could change all of these and 110 00:06:36.006 --> 00:06:40.938 we could put a name right here, and then we could put name and then continue on. 111 00:06:40.938 --> 00:06:46.776 But that means that all of our attributes have to know how a character is created. 112 00:06:46.776 --> 00:06:50.767 Well, that's fine, but that creates what you'll hear a lot of developers call 113 00:06:50.767 --> 00:06:53.940 tightly coupled code, or a tightly coupled design. 114 00:06:53.940 --> 00:06:56.240 We want to create code that's loosely coupled, so 115 00:06:56.240 --> 00:06:59.460 that it becomes easier to mix and match things around. 116 00:06:59.460 --> 00:07:05.350 So instead, let's go change how the name argument in Character is defined. 117 00:07:05.350 --> 00:07:10.230 And let's make it a keyword argument, right? 118 00:07:10.230 --> 00:07:12.150 Because we provided a default value. 119 00:07:12.150 --> 00:07:15.490 All we have to do is add the equals and the empty string. 120 00:07:15.490 --> 00:07:18.790 But we wanna make sure that there's a name that's set. 121 00:07:18.790 --> 00:07:21.750 So let's add a check and an exception. 122 00:07:21.750 --> 00:07:27.585 So if not name, and then we're going to raise ValueError, 123 00:07:27.585 --> 00:07:31.094 and we'll say, name is required. 124 00:07:33.170 --> 00:07:36.100 And then let's try to create our Thief right now. 125 00:07:38.510 --> 00:07:40.430 And we get our ValueError, name is required. 126 00:07:40.430 --> 00:07:43.500 So now when we create our thief, let's go right here and 127 00:07:43.500 --> 00:07:44.900 let's say name is equal to Kenneth. 128 00:07:46.010 --> 00:07:50.640 So now, when we explicitly set this parameter, and remember explicit is better 129 00:07:50.640 --> 00:07:55.960 than implicit, our whole character works just like we expected it to. 130 00:07:55.960 --> 00:07:57.200 So great work everyone. 131 00:07:58.520 --> 00:08:01.540 You'll hear a lot of developers talk about whether something is loosely or 132 00:08:01.540 --> 00:08:02.790 tightly coupled. 133 00:08:02.790 --> 00:08:06.650 Usually they'll complain about something being tightly coupled and for good reason. 134 00:08:06.650 --> 00:08:09.260 Code that relies heavily on other code can make it very 135 00:08:09.260 --> 00:08:12.390 difficult to add in the functionality you want and need. 136 00:08:12.390 --> 00:08:16.050 For instance, imagine you had code to send messages to users of your app. 137 00:08:16.050 --> 00:08:19.680 If your message sending code always used a single mechanism for delivering those 138 00:08:19.680 --> 00:08:24.610 messages, like email, it would be really hard to add in SMS or push notifications. 139 00:08:24.610 --> 00:08:27.750 If the code is more loosely coupled though and just expected there to be a send 140 00:08:27.750 --> 00:08:31.060 message method, you could swap out the backend much more easily.