WEBVTT 1 00:00:00.520 --> 00:00:01.940 Hi guys and welcome back. 2 00:00:01.940 --> 00:00:04.600 In this video, we're going to talk about static methods 3 00:00:04.600 --> 00:00:06.140 and class methods. 4 00:00:06.140 --> 00:00:08.990 These can be a little bit confusing so let's get started. 5 00:00:08.990 --> 00:00:12.550 Here, we've got a class that I have called ClassTest. 6 00:00:12.550 --> 00:00:15.040 This is just to show you how these things work. 7 00:00:15.040 --> 00:00:18.160 And then we have defined a method. 8 00:00:18.160 --> 00:00:21.630 We know it's a method because it is a function, 9 00:00:21.630 --> 00:00:23.280 which starts with a def keyword, 10 00:00:23.280 --> 00:00:27.040 and it has self as a first parameter. 11 00:00:27.040 --> 00:00:30.950 All functions inside the class that use the object 12 00:00:30.950 --> 00:00:33.380 as the first parameter, 13 00:00:33.380 --> 00:00:35.673 are called instance methods. 14 00:00:36.770 --> 00:00:38.860 And this instance_method, 15 00:00:38.860 --> 00:00:41.030 prints that you've called the instance_method. 16 00:00:41.030 --> 00:00:44.210 How would you call this method if you wanted to call it? 17 00:00:44.210 --> 00:00:46.640 You have two options. 18 00:00:46.640 --> 00:00:50.610 Okay, the first option is to do something like, 19 00:00:50.610 --> 00:00:55.610 test = ClassTest, and create a new object of type ClassTest. 20 00:00:56.780 --> 00:00:59.780 Notice that we don't have an init method in this class, 21 00:00:59.780 --> 00:01:00.810 but that's okay. 22 00:01:00.810 --> 00:01:02.105 If you don't have an init method, 23 00:01:02.105 --> 00:01:03.071 that just means that you 24 00:01:03.071 --> 00:01:05.380 don't have any initialization to do, 25 00:01:05.380 --> 00:01:08.470 but the self is still created 26 00:01:08.470 --> 00:01:10.310 and you still get a new object. 27 00:01:10.310 --> 00:01:13.050 And make it equal to your variable. 28 00:01:13.050 --> 00:01:14.210 Here, we're creating a new object 29 00:01:14.210 --> 00:01:18.170 and you can do test.instance_method, or as we know it, 30 00:01:18.170 --> 00:01:20.770 you can ClassTest.instance_method 31 00:01:20.770 --> 00:01:22.630 with test as the argument. 32 00:01:22.630 --> 00:01:24.610 Both of these things are exactly the same. 33 00:01:24.610 --> 00:01:27.670 If you run this code, you'll get that you've called 34 00:01:27.670 --> 00:01:30.430 the instance_method of this object. 35 00:01:30.430 --> 00:01:33.770 Notice that we are printing the object self here, 36 00:01:33.770 --> 00:01:35.630 and as we saw earlier on, 37 00:01:35.630 --> 00:01:38.590 you get back this ugly print out. 38 00:01:38.590 --> 00:01:40.470 If you wanted it to be a little bit nicer, 39 00:01:40.470 --> 00:01:44.050 you would have to implement your str or repr methods, 40 00:01:44.050 --> 00:01:45.050 one of the two. 41 00:01:45.050 --> 00:01:49.150 But for now, we have called the instance_method two times. 42 00:01:49.150 --> 00:01:52.800 It is called an instance_method because you call it 43 00:01:52.800 --> 00:01:55.430 on a class instance. 44 00:01:55.430 --> 00:01:58.600 The name instance, it means the same thing, an object. 45 00:01:58.600 --> 00:02:00.980 What we're doing here is we're creating an object 46 00:02:00.980 --> 00:02:01.880 of type ClassTest. 47 00:02:03.220 --> 00:02:04.530 You can also say that you're creating 48 00:02:04.530 --> 00:02:06.410 an instance of ClassTest. 49 00:02:06.410 --> 00:02:08.170 They mean the same thing. 50 00:02:08.170 --> 00:02:10.653 That is why these are called instance methods. 51 00:02:11.750 --> 00:02:16.200 Instance methods need the object in order to call them. 52 00:02:16.200 --> 00:02:20.290 The next type is called a class method. 53 00:02:20.290 --> 00:02:23.280 Here, you can define another method. 54 00:02:23.280 --> 00:02:28.280 But now instead of the instance, or the object, self, 55 00:02:28.360 --> 00:02:31.000 it actually takes a different parameter 56 00:02:31.000 --> 00:02:33.610 that we usually in Python, call cls, 57 00:02:33.610 --> 00:02:35.550 but you can call this parameter whatever you want, 58 00:02:35.550 --> 00:02:37.470 the value will still be the same no matter 59 00:02:37.470 --> 00:02:39.520 what you call this parameter. 60 00:02:39.520 --> 00:02:42.740 What this parameter will be in a class method, 61 00:02:42.740 --> 00:02:45.870 that is when you put this at @classmethod on top 62 00:02:45.870 --> 00:02:50.573 of the method definition, is this will be the class itself. 63 00:02:51.930 --> 00:02:54.510 Let me show you how this works. 64 00:02:54.510 --> 00:02:57.380 Called class_method of {cls}. 65 00:02:57.380 --> 00:02:59.740 I'll just print the parameter there, 66 00:02:59.740 --> 00:03:02.130 and then, because it is a class method, 67 00:03:02.130 --> 00:03:03.370 it's not an instance method, 68 00:03:03.370 --> 00:03:05.480 you no longer need an instance. 69 00:03:05.480 --> 00:03:06.800 That means that you can just do, 70 00:03:06.800 --> 00:03:10.960 ClassTest.class_method, and that's it, 71 00:03:10.960 --> 00:03:13.040 you don't have to pass in anything in there 72 00:03:13.040 --> 00:03:16.080 because we no longer need the object. 73 00:03:16.080 --> 00:03:17.980 Python is smart enough that when you do 74 00:03:17.980 --> 00:03:21.820 ClassTest.class_method and you don't pass anything in there, 75 00:03:21.820 --> 00:03:25.940 Python will actually pass ClassTest in there. 76 00:03:25.940 --> 00:03:29.920 So, actually cls is ClassTest, 77 00:03:29.920 --> 00:03:32.443 because that is what you called the method on. 78 00:03:33.520 --> 00:03:34.620 That is how this works. 79 00:03:34.620 --> 00:03:36.650 When you do ClassTest.class_method, 80 00:03:36.650 --> 00:03:40.040 given that you have put this @classmethod on top. 81 00:03:40.040 --> 00:03:41.710 We're going to learn what this is later on. 82 00:03:41.710 --> 00:03:43.450 Don't worry about it too much. 83 00:03:43.450 --> 00:03:47.600 Then Python will pass in the class as the argument 84 00:03:47.600 --> 00:03:48.793 to this parameter. 85 00:03:49.740 --> 00:03:52.110 If we save and play, 86 00:03:52.110 --> 00:03:53.910 you'll see that now you get that you've called 87 00:03:53.910 --> 00:03:58.120 the class_method of this class called ClassTest. 88 00:03:58.120 --> 00:04:00.760 Don't worry too much about the __main__, 89 00:04:00.760 --> 00:04:03.370 we will learn about that later on if it becomes relevant. 90 00:04:03.370 --> 00:04:06.160 It's largely irrelevant to most Python programmes. 91 00:04:06.160 --> 00:04:08.430 This just means that you've called the class_method 92 00:04:08.430 --> 00:04:09.690 of this class. 93 00:04:09.690 --> 00:04:11.850 We're going to find used cases for class_methods 94 00:04:11.850 --> 00:04:14.220 in just a little bit later on in this video. 95 00:04:14.220 --> 00:04:17.510 Finally, the last option is the @staticmethod. 96 00:04:18.426 --> 00:04:21.804 And this defines a static method that I'm going to call 97 00:04:21.804 --> 00:04:22.760 static_method. 98 00:04:22.760 --> 00:04:24.340 Again, you can call it whatever you want 99 00:04:24.340 --> 00:04:28.580 and now I'm not going to put anything inside the brackets. 100 00:04:28.580 --> 00:04:31.993 Here, we're going to do "Called static_method." 101 00:04:32.950 --> 00:04:35.880 In a static method, that is a method 102 00:04:35.880 --> 00:04:39.370 that doesn't have a parameter cls or self, 103 00:04:39.370 --> 00:04:42.370 and that has @staticmethod on top. 104 00:04:42.370 --> 00:04:45.710 These methods don't get anything when you call them. 105 00:04:45.710 --> 00:04:48.210 The class method gets the class normally 106 00:04:48.210 --> 00:04:50.090 and you can print it out or use it. 107 00:04:50.090 --> 00:04:52.900 The instance_methods gets the instance or the object 108 00:04:52.900 --> 00:04:55.360 and you can print it out or use it in them. 109 00:04:55.360 --> 00:04:58.560 But static methods don't get either of those things. 110 00:04:58.560 --> 00:05:00.710 And you can call them in the same way 111 00:05:00.710 --> 00:05:03.720 just by doing static_method inside ClassTest 112 00:05:03.720 --> 00:05:07.330 or ClassTest.static_method but Python will not put 113 00:05:07.330 --> 00:05:09.040 the ClassTest in the brackets. 114 00:05:09.040 --> 00:05:11.140 It will just call that method. 115 00:05:11.140 --> 00:05:13.480 This really isn't a method. 116 00:05:13.480 --> 00:05:16.710 It's just a function that you've placed inside a class. 117 00:05:16.710 --> 00:05:18.840 We should still call it a method but it doesn't have 118 00:05:18.840 --> 00:05:21.630 any information about the class or the object 119 00:05:21.630 --> 00:05:24.560 so it's really just its own separate function 120 00:05:24.560 --> 00:05:26.800 that lives inside the class. 121 00:05:26.800 --> 00:05:29.400 If you want a function inside the class 122 00:05:29.400 --> 00:05:31.410 that doesn't use the class for anything, 123 00:05:31.410 --> 00:05:35.630 or the instance, you can decorate it with @staticmethod. 124 00:05:35.630 --> 00:05:38.600 If you want a method that uses the class for something, 125 00:05:38.600 --> 00:05:41.500 then you can decorate it @classmethod. 126 00:05:41.500 --> 00:05:42.960 And if you want to use the object, 127 00:05:42.960 --> 00:05:45.820 or if you wanna create any other type of instance_method, 128 00:05:45.820 --> 00:05:47.940 then just don't put anything on top. 129 00:05:47.940 --> 00:05:50.240 No @classmethod or @staticmethod 130 00:05:50.240 --> 00:05:52.610 and make sure to include your parameter there. 131 00:05:52.610 --> 00:05:55.010 Again, if you call this like that and you press play, 132 00:05:55.010 --> 00:05:57.720 you just get Called static_method. 133 00:05:57.720 --> 00:05:59.683 So, what are these used for? 134 00:06:00.530 --> 00:06:02.880 Instance methods are used for most things. 135 00:06:02.880 --> 00:06:05.800 When you wanna produce an action that uses the data 136 00:06:05.800 --> 00:06:08.340 inside the object that you created earlier on for example, 137 00:06:08.340 --> 00:06:11.230 that is when instance methods would get used. 138 00:06:11.230 --> 00:06:13.620 Also, if you wanna call a method to modify 139 00:06:13.620 --> 00:06:16.110 some sort of data inside self or the object, 140 00:06:16.110 --> 00:06:17.840 then you would also use an instance method. 141 00:06:17.840 --> 00:06:21.930 Class methods are used often as factories 142 00:06:21.930 --> 00:06:24.130 and I'm going to show you what that is in a second. 143 00:06:24.130 --> 00:06:27.570 And finally, static_methods are used to just place a method 144 00:06:27.570 --> 00:06:28.670 inside a class. 145 00:06:28.670 --> 00:06:31.270 Because you feel like it belongs there for some reason. 146 00:06:31.270 --> 00:06:33.330 For you as a developer, you wanna put that method in there 147 00:06:33.330 --> 00:06:36.920 because it makes sense logically for code organisation 148 00:06:36.920 --> 00:06:39.410 or something like that, then you can use that. 149 00:06:39.410 --> 00:06:41.040 I'll say though that most of the time, 150 00:06:41.040 --> 00:06:43.610 you'll be using class methods and instance methods. 151 00:06:43.610 --> 00:06:46.010 You won't be using static methods all that much. 152 00:06:46.900 --> 00:06:49.570 Let's start with our factory example 153 00:06:49.570 --> 00:06:52.440 that is going to show you how you might use a class method. 154 00:06:52.440 --> 00:06:54.610 This example is gonna be a little bit tricky 155 00:06:54.610 --> 00:06:56.010 so please bear with me for a second 156 00:06:56.010 --> 00:06:58.930 while I explain first what I've done here. 157 00:06:58.930 --> 00:07:01.290 In a class, as well as methods, 158 00:07:01.290 --> 00:07:03.670 you can also put variables 159 00:07:03.670 --> 00:07:06.610 and these become class properties. 160 00:07:06.610 --> 00:07:10.270 If you wanted to print out this tuple here, 161 00:07:10.270 --> 00:07:13.680 all you have to do is access the TYPES tuple 162 00:07:13.680 --> 00:07:15.660 inside the Book class. 163 00:07:15.660 --> 00:07:18.690 You would do Book.TYPES, 164 00:07:18.690 --> 00:07:20.930 and that is how you access this tuple there. 165 00:07:20.930 --> 00:07:22.090 You can print it out 166 00:07:22.090 --> 00:07:24.793 and you can see that you get hardcover and paperback. 167 00:07:25.750 --> 00:07:29.130 We have some data stored inside the class, 168 00:07:29.130 --> 00:07:30.400 which is this tuple here, 169 00:07:30.400 --> 00:07:33.290 and a reason why you might put some data inside a class, 170 00:07:33.290 --> 00:07:35.650 as opposed to putting it outside the class, 171 00:07:35.650 --> 00:07:37.650 is because you feel like it belongs there 172 00:07:37.650 --> 00:07:40.030 or only the Book class is going to use it, 173 00:07:40.030 --> 00:07:41.820 or maybe there is some sort of reason, 174 00:07:41.820 --> 00:07:44.410 logical reason to put that data in there. 175 00:07:44.410 --> 00:07:46.950 Here I'm creating a class that talks about Books. 176 00:07:46.950 --> 00:07:50.053 So, it makes sense to have book types inside there. 177 00:07:51.040 --> 00:07:53.690 Then we're going to create an init method for this class. 178 00:07:53.690 --> 00:07:55.660 Remember, because this is an instance method 179 00:07:55.660 --> 00:07:57.920 it creates an instance and gives it back to you, 180 00:07:57.920 --> 00:07:59.720 you need the self parameter there. 181 00:07:59.720 --> 00:08:01.830 You can call self whatever you want, once again, 182 00:08:01.830 --> 00:08:04.130 but the convention in Python is to call it self. 183 00:08:04.130 --> 00:08:06.610 And then we're going to be creating objects 184 00:08:06.610 --> 00:08:09.280 of type Book that have three things. 185 00:08:09.280 --> 00:08:12.570 A name, a book type, and a weight. 186 00:08:12.570 --> 00:08:14.850 So, we will do self.name = name, 187 00:08:14.850 --> 00:08:16.183 Self.book_type = book_type, 188 00:08:17.610 --> 00:08:19.470 and self.weight = weight. 189 00:08:19.470 --> 00:08:21.460 This is a very common thing in Python 190 00:08:21.460 --> 00:08:23.640 to create an object with three different values 191 00:08:23.640 --> 00:08:26.280 that you then store each one inside a property 192 00:08:26.280 --> 00:08:27.970 of the object itself. 193 00:08:27.970 --> 00:08:30.070 Just to recap, if you were to create a variable 194 00:08:30.070 --> 00:08:32.260 such as Book, and make it an object, 195 00:08:32.260 --> 00:08:35.410 then you will need to pass in some information, 196 00:08:35.410 --> 00:08:39.230 let's say, "Harry Potter", "hardcover", and 1500, 197 00:08:39.230 --> 00:08:42.200 then you can print book.name 198 00:08:42.200 --> 00:08:43.640 and what that's going to do is it's going 199 00:08:43.640 --> 00:08:47.210 to pass in "Harry Potter" as the value for this parameter. 200 00:08:47.210 --> 00:08:50.040 Then that is going to be assigned to the name property 201 00:08:50.040 --> 00:08:52.400 of the self object, which is essentially 202 00:08:52.400 --> 00:08:54.730 an empty container at this stage, 203 00:08:54.730 --> 00:08:56.810 and then we're going to print it out down here. 204 00:08:56.810 --> 00:08:58.340 So if we press play, 205 00:08:58.340 --> 00:08:59.820 you'll see that "Harry Potter" comes out. 206 00:08:59.820 --> 00:09:01.560 That's how the data is flowing through 207 00:09:01.560 --> 00:09:03.730 this system at this stage. 208 00:09:03.730 --> 00:09:05.990 Then I'm also going to create a repr method 209 00:09:05.990 --> 00:09:07.040 so that it's a little bit easier 210 00:09:07.040 --> 00:09:08.660 to work with these books. 211 00:09:08.660 --> 00:09:12.430 And we are going to return a Book with this name. 212 00:09:12.430 --> 00:09:13.800 It is this Book type 213 00:09:13.800 --> 00:09:18.590 and it's weighing {self.weight}g>. 214 00:09:18.590 --> 00:09:22.170 This is a representation of the book that would allow us, 215 00:09:22.170 --> 00:09:25.050 with all the data included inside, 216 00:09:25.050 --> 00:09:27.440 to recreate a book object if we wanted to. 217 00:09:27.440 --> 00:09:29.920 Remember, that is the purpose of the repr method. 218 00:09:29.920 --> 00:09:32.090 If you wanted to just print the book out nicely 219 00:09:32.090 --> 00:09:33.420 for users to read, 220 00:09:33.420 --> 00:09:36.500 then you could use the str method instead. 221 00:09:36.500 --> 00:09:37.930 Now instead of putting in book.name, 222 00:09:37.930 --> 00:09:40.780 we're just going to print book and I will press play 223 00:09:40.780 --> 00:09:42.390 and show you what the output is. 224 00:09:42.390 --> 00:09:43.747 Here's the book, "Harry Potter." 225 00:09:43.747 --> 00:09:47.190 It's a hardcover, weighing 1500 grammes. 226 00:09:47.190 --> 00:09:51.030 Now we come into the factories. 227 00:09:51.030 --> 00:09:52.810 Here's where we're gonna use class_methods. 228 00:09:52.810 --> 00:09:56.660 I wanna avoid, when I'm creating a new book object, 229 00:09:56.660 --> 00:09:58.400 when I'm calling the init method, 230 00:09:58.400 --> 00:10:01.910 I want to avoid passing in this "hardcover" string 231 00:10:01.910 --> 00:10:04.290 because I only want to be able to create books 232 00:10:04.290 --> 00:10:06.760 that are either hardcover or paperback, 233 00:10:06.760 --> 00:10:08.810 I wanna make sure that when I create a book, 234 00:10:08.810 --> 00:10:11.220 I use one of these two types. 235 00:10:11.220 --> 00:10:15.090 Right now, I can pass in comic book if I wanted to here 236 00:10:15.090 --> 00:10:17.840 and that would be totally fine because again, 237 00:10:17.840 --> 00:10:20.990 the data, this string here, becomes the value of book_type. 238 00:10:20.990 --> 00:10:23.470 Book_type gets assigned to self.book_type, 239 00:10:23.470 --> 00:10:24.580 and that gets used down here. 240 00:10:24.580 --> 00:10:26.770 There is no check for this, 241 00:10:26.770 --> 00:10:28.703 nothing is using this at the moment. 242 00:10:29.610 --> 00:10:32.920 What I'm going to do is I'm going to create a method 243 00:10:32.920 --> 00:10:36.360 that will take in the name and the weight 244 00:10:36.360 --> 00:10:40.340 and will create a new book object of type hardcover. 245 00:10:40.340 --> 00:10:44.063 I'm going to call this @classmethod hardcover, 246 00:10:45.450 --> 00:10:46.940 and again, because it is a class method, 247 00:10:46.940 --> 00:10:49.170 it takes in the class as the first parameter, 248 00:10:49.170 --> 00:10:51.080 usually called that cls in Python. 249 00:10:51.080 --> 00:10:53.220 And that is going to take in the name 250 00:10:53.220 --> 00:10:55.370 and the page weight, 251 00:10:55.370 --> 00:10:59.500 and what it's going to do is it is going to return a book 252 00:10:59.500 --> 00:11:02.310 with the name as the first argument, 253 00:11:02.310 --> 00:11:04.030 which then goes into the init method. 254 00:11:04.030 --> 00:11:09.030 Book.TYPES[0] as the second argument. 255 00:11:09.680 --> 00:11:12.180 Remember, Book.TYPES gives us this tuple. 256 00:11:12.180 --> 00:11:15.700 Book.TYPES[0] gives us the hardcover. 257 00:11:15.700 --> 00:11:18.957 And finally, the page_weight + 100 258 00:11:19.901 --> 00:11:21.940 for the weight of the book. 259 00:11:21.940 --> 00:11:23.690 I'm adding 100 because it's a hardcover 260 00:11:23.690 --> 00:11:25.290 so it's probably going to be a little heavier 261 00:11:25.290 --> 00:11:26.810 than a paperback. 262 00:11:26.810 --> 00:11:27.870 Hopefully this makes sense. 263 00:11:27.870 --> 00:11:30.710 It is a little bit confusing because you are using 264 00:11:30.710 --> 00:11:35.080 the class inside a method defined inside the class. 265 00:11:35.080 --> 00:11:36.750 Which I know is a little bit weird, 266 00:11:36.750 --> 00:11:40.700 but that is how you can create a new object 267 00:11:40.700 --> 00:11:42.233 inside of a class. 268 00:11:42.233 --> 00:11:44.630 This is something you can totally do. 269 00:11:44.630 --> 00:11:46.060 And because it is a class method, 270 00:11:46.060 --> 00:11:48.860 you no longer need to create your own object first. 271 00:11:48.860 --> 00:11:49.860 All you have to do now is say, 272 00:11:49.860 --> 00:11:53.640 Book.hardcover and pass in here "Harry Potter" 273 00:11:53.640 --> 00:11:56.370 and the page weight which was 1500. 274 00:11:56.370 --> 00:11:59.650 Notice that this hardcover method takes in the name 275 00:11:59.650 --> 00:12:02.360 and the page weight but it does not take in a type. 276 00:12:02.360 --> 00:12:04.730 The type is added inside the method, 277 00:12:04.730 --> 00:12:07.520 you don't have to pass it in as an argument. 278 00:12:07.520 --> 00:12:09.240 If I save and run that, 279 00:12:09.240 --> 00:12:11.130 you can see that now you get a book "Harry Potter," 280 00:12:11.130 --> 00:12:13.770 which is a hardcover, and weighs 1600 grammes. 281 00:12:13.770 --> 00:12:17.230 Let's do the same thing for the paperback. 282 00:12:17.230 --> 00:12:18.860 Only now instead of Book.TYPES[0], 283 00:12:18.860 --> 00:12:20.330 I'm going to do Book.TYPES[1] 284 00:12:20.330 --> 00:12:22.853 and I'm going to remove this + 100. 285 00:12:23.740 --> 00:12:26.070 So now, if we wanted to create a softcover book, 286 00:12:26.070 --> 00:12:27.630 or a paperback, you can say something like, 287 00:12:27.630 --> 00:12:30.147 light = Book.paperback("Python 101"), 288 00:12:31.220 --> 00:12:33.360 and you can say for example, 600. 289 00:12:33.360 --> 00:12:35.890 If you then print the light book as well, 290 00:12:35.890 --> 00:12:38.460 you'll see that you get two books printed out now. 291 00:12:38.460 --> 00:12:41.290 Book "Harry Potter," which is hardcover, weighing 1600 grammes 292 00:12:41.290 --> 00:12:43.440 and Book "Python 101," which is a paperback, 293 00:12:43.440 --> 00:12:45.190 weighing 600 grammes. 294 00:12:45.190 --> 00:12:49.390 This is a very, very common way of using class methods 295 00:12:49.390 --> 00:12:51.700 because you have access to the class itself 296 00:12:51.700 --> 00:12:54.790 inside the method, that means that it is a perfect place 297 00:12:54.790 --> 00:12:59.500 to be creating new objects by using that class. 298 00:12:59.500 --> 00:13:01.850 With that said though, notice that I'm using Book here 299 00:13:01.850 --> 00:13:03.810 and I'm not using cls anywhere. 300 00:13:03.810 --> 00:13:07.580 Book is the class as we saw earlier on. 301 00:13:07.580 --> 00:13:10.300 And cls is also the class. 302 00:13:10.300 --> 00:13:11.950 They are interchangeable. 303 00:13:11.950 --> 00:13:15.590 Instead of Book, you can put cls in there. 304 00:13:15.590 --> 00:13:19.230 And instead of Book down here, you can put cls in there. 305 00:13:19.230 --> 00:13:20.700 You should do that. 306 00:13:20.700 --> 00:13:24.490 Use cls instead of Book and that will come in handy 307 00:13:24.490 --> 00:13:26.510 when you look at inheritance, 308 00:13:26.510 --> 00:13:28.330 which we will look at later on. 309 00:13:28.330 --> 00:13:30.420 Just because using cls gives you a little bit more 310 00:13:30.420 --> 00:13:32.650 flexibility down the line. 311 00:13:32.650 --> 00:13:35.670 Do use cls there since you've got access to it 312 00:13:35.670 --> 00:13:37.960 and if you were creating a static method 313 00:13:37.960 --> 00:13:39.050 instead of a class method, 314 00:13:39.050 --> 00:13:40.820 you would have to use book class 315 00:13:40.820 --> 00:13:42.680 because you wouldn't have cls. 316 00:13:42.680 --> 00:13:45.150 If you want to use cls use a class method, 317 00:13:45.150 --> 00:13:48.450 use the paramter, and you can create new objects 318 00:13:48.450 --> 00:13:50.810 and return them or use them however you like. 319 00:13:50.810 --> 00:13:52.460 Hopefully this makes sense. 320 00:13:52.460 --> 00:13:54.360 I know that it's a little bit confusing 321 00:13:54.360 --> 00:13:56.400 looking at class methods and static methods 322 00:13:56.400 --> 00:13:57.930 and it's been a bit of a long video 323 00:13:57.930 --> 00:13:59.630 but hopefully it was helpful. 324 00:13:59.630 --> 00:14:02.280 Hope you enjoyed it and I'll see you in the next one.