1 1 00:00:00,130 --> 00:00:01,970 Hi guys and welcome back. 2 2 00:00:01,970 --> 00:00:03,890 In this video we're gonna talk about 3 3 00:00:03,890 --> 00:00:06,140 object oriented programming. 4 4 00:00:06,140 --> 00:00:08,790 Object oriented programming is a bit confusing 5 5 00:00:08,790 --> 00:00:11,070 when you get started, so if you've never seen 6 6 00:00:11,070 --> 00:00:13,950 object oriented programming before, just take it easy 7 7 00:00:13,950 --> 00:00:16,410 with the next few videos, watch them a couple of times 8 8 00:00:16,410 --> 00:00:18,330 if you need to, ask any questions in the course 9 9 00:00:18,330 --> 00:00:22,000 of the Q and A, if necessary we'll be there to help you out. 10 10 00:00:22,000 --> 00:00:24,780 Object oriented programming allows us as developers 11 11 00:00:24,780 --> 00:00:28,260 to write code in a slightly different way 12 12 00:00:28,260 --> 00:00:30,250 than we would write if we didn't have 13 13 00:00:30,250 --> 00:00:32,140 object oriented programming. 14 14 00:00:32,140 --> 00:00:34,900 The purpose of object oriented programming 15 15 00:00:34,900 --> 00:00:37,274 is to make our life as developers simpler 16 16 00:00:37,274 --> 00:00:41,641 by allowing us to write code that looks like 17 17 00:00:41,641 --> 00:00:44,480 what we would work with in the real world 18 18 00:00:44,480 --> 00:00:46,750 if we were talking about, you know, 19 19 00:00:46,750 --> 00:00:49,110 real world things like chairs and tables 20 20 00:00:49,110 --> 00:00:50,640 and printers and things like that, 21 21 00:00:50,640 --> 00:00:53,860 as opposed to code and data passing 22 22 00:00:53,860 --> 00:00:55,860 from one function to another. 23 23 00:00:55,860 --> 00:00:58,250 So that is the purpose of object oriented programming. 24 24 00:00:58,250 --> 00:00:59,990 And in this video we're going to look at how 25 25 00:00:59,990 --> 00:01:01,163 it works in Python. 26 26 00:01:02,260 --> 00:01:05,820 Let's say that you've got a dictionary like this one here 27 27 00:01:05,820 --> 00:01:09,370 which shows some information about a student. 28 28 00:01:09,370 --> 00:01:12,920 Now clearly this thing here is not a student, 29 29 00:01:12,920 --> 00:01:15,160 it is a dictionary that has some data. 30 30 00:01:15,160 --> 00:01:18,160 And as we know, programming is all about data, 31 31 00:01:18,160 --> 00:01:20,860 passing data from one place to another and so forth. 32 32 00:01:20,860 --> 00:01:23,500 So what we've got here is some data that is probably 33 33 00:01:23,500 --> 00:01:25,810 about a student somewhere in our classroom 34 34 00:01:25,810 --> 00:01:27,113 or something like that. 35 35 00:01:27,970 --> 00:01:31,012 Then we've got a function that takes in a sequence 36 36 00:01:31,012 --> 00:01:35,130 and adds the entire sequence together and divides it 37 37 00:01:35,130 --> 00:01:37,690 by the length of the sequence and then returns that. 38 38 00:01:37,690 --> 00:01:40,630 So it gives you the average of a sequence. 39 39 00:01:40,630 --> 00:01:43,120 For example we could use it to calculate the average 40 40 00:01:43,120 --> 00:01:45,180 grade of Rolf. 41 41 00:01:45,180 --> 00:01:46,520 How would you do that? 42 42 00:01:46,520 --> 00:01:48,739 Well you would have to use the function 43 43 00:01:48,739 --> 00:01:52,160 and give to it Rolf's grades. 44 44 00:01:52,160 --> 00:01:57,160 So you do average student grades, like that. 45 45 00:01:58,380 --> 00:02:01,540 So if we run that you'll see that we get out 46 46 00:02:01,540 --> 00:02:05,760 the value 88.0 which is the average grade. 47 47 00:02:05,760 --> 00:02:09,230 However, there is something about this function 48 48 00:02:09,230 --> 00:02:13,190 which is very important when you are thinking 49 49 00:02:13,190 --> 00:02:14,490 about object oriented programming, 50 50 00:02:14,490 --> 00:02:17,236 which is that this function doesn't know anything 51 51 00:02:17,236 --> 00:02:20,761 about the student. 52 52 00:02:20,761 --> 00:02:25,050 The function only operates on the input that it receives 53 53 00:02:25,050 --> 00:02:27,510 and that could be a set of student grades 54 54 00:02:27,510 --> 00:02:29,393 or it could be something else. 55 55 00:02:30,713 --> 00:02:34,850 So when we as developers are talking specifically 56 56 00:02:34,850 --> 00:02:37,460 about a student and we want to calculate specifically 57 57 00:02:37,460 --> 00:02:42,460 the average student grade for Rolf, it is much nicer 58 58 00:02:42,690 --> 00:02:46,435 if we can say hey student, what's your average 59 59 00:02:46,435 --> 00:02:51,170 as opposed to get the average of this sequence 60 60 00:02:51,170 --> 00:02:54,490 that could or could not be related to the student. 61 61 00:02:54,490 --> 00:02:59,462 So basically what I want to do is student.average. 62 62 00:02:59,462 --> 00:03:02,240 This is what object oriented programming 63 63 00:03:02,240 --> 00:03:04,430 will allow us to do. 64 64 00:03:04,430 --> 00:03:09,130 But in order to do that, student cannot be a dictionary 65 65 00:03:09,130 --> 00:03:12,180 because dictionaries you can't do that on. 66 66 00:03:12,180 --> 00:03:16,330 You have to code your own thing in Python that will 67 67 00:03:16,330 --> 00:03:21,180 allow you to call the average method inside it, 68 68 00:03:21,180 --> 00:03:24,390 and that will give you the average of the student. 69 69 00:03:24,390 --> 00:03:26,820 So it is a very different approach, 70 70 00:03:26,820 --> 00:03:30,760 and it is not necessarily superior, 71 71 00:03:30,760 --> 00:03:32,280 but it is different and allows 72 72 00:03:32,280 --> 00:03:35,000 you to think of your programmes in a different way. 73 73 00:03:35,000 --> 00:03:37,920 So let's rewrite this example here using object 74 74 00:03:37,920 --> 00:03:41,830 oriented programming so you'll have a look at the syntax. 75 75 00:03:41,830 --> 00:03:43,470 The syntax for object oriented programming 76 76 00:03:43,470 --> 00:03:46,900 or to define a class in Python is to type out a keyword 77 77 00:03:46,900 --> 00:03:50,160 class, and then the name of your class. 78 78 00:03:50,160 --> 00:03:53,560 So a class is a definition of something, 79 79 00:03:53,560 --> 00:03:56,680 but it doesn't create a particular student here, 80 80 00:03:56,680 --> 00:03:58,980 we're only defining how a student will behave. 81 81 00:04:00,080 --> 00:04:03,870 So you can say inside the function, 82 82 00:04:03,870 --> 00:04:06,680 notice that there are four spaces of indentation, 83 83 00:04:06,680 --> 00:04:08,450 you can define functions. 84 84 00:04:08,450 --> 00:04:10,760 So you can define a special function called 85 85 00:04:10,760 --> 00:04:15,090 the underscore underscore init underscore underscore. 86 86 00:04:15,090 --> 00:04:17,500 So this function name is very important, 87 87 00:04:17,500 --> 00:04:19,010 and it has two underscores at the start 88 88 00:04:19,010 --> 00:04:20,520 and two at the end. 89 89 00:04:20,520 --> 00:04:23,880 And then you put your brackets and in here we're going 90 90 00:04:23,880 --> 00:04:26,040 to type out self. 91 91 00:04:26,040 --> 00:04:28,610 Although this is again just a variable name 92 92 00:04:28,610 --> 00:04:30,470 like in every other function and you can call it 93 93 00:04:30,470 --> 00:04:31,770 whatever you want, it doesn't have to be self 94 94 00:04:31,770 --> 00:04:35,023 if you don't want, but self is the convention in Python. 95 95 00:04:36,060 --> 00:04:39,170 Then in the body of the function you can define 96 96 00:04:39,170 --> 00:04:40,520 anything you want. 97 97 00:04:40,520 --> 00:04:44,820 For example, self.name is going to be Rolf. 98 98 00:04:44,820 --> 00:04:48,230 And what this is doing is it is taking whatever self is 99 99 00:04:50,070 --> 00:04:54,390 and it is accessing the name property inside of self. 100 100 00:04:54,390 --> 00:04:57,130 So here we're using the dot notation 101 101 00:04:57,130 --> 00:04:59,420 to access something inside of self, 102 102 00:04:59,420 --> 00:05:02,060 and what we're accessing is the name property. 103 103 00:05:02,060 --> 00:05:04,970 And then we're giving it a value of Rolf. 104 104 00:05:04,970 --> 00:05:09,600 What that means is that when we use this class 105 105 00:05:09,600 --> 00:05:12,950 to create something, that thing is going 106 106 00:05:12,950 --> 00:05:14,180 to have a name of Rolf. 107 107 00:05:14,180 --> 00:05:17,310 So here's how you create a thing from a class. 108 108 00:05:17,310 --> 00:05:20,297 We can say something like student, notice that now 109 109 00:05:20,297 --> 00:05:21,580 this is lowercase because this is a new variable 110 110 00:05:21,580 --> 00:05:23,400 that we're creating right now, 111 111 00:05:23,400 --> 00:05:28,400 is a student, which is uppercase S because this the class. 112 112 00:05:28,900 --> 00:05:31,560 And now we're going to tell it to use the class 113 113 00:05:31,560 --> 00:05:35,160 to create what's called an object in Python 114 114 00:05:35,160 --> 00:05:38,500 to create a new thing that behaves 115 115 00:05:38,500 --> 00:05:40,930 like what this class defines. 116 116 00:05:40,930 --> 00:05:44,380 So when you do this Python creates a new 117 117 00:05:44,380 --> 00:05:47,460 essentially empty container if you will 118 118 00:05:47,460 --> 00:05:50,070 and it runs the init method. 119 119 00:05:50,070 --> 00:05:52,260 By the way it is a method and not a function 120 120 00:05:52,260 --> 00:05:54,270 because it is inside of a class. 121 121 00:05:54,270 --> 00:05:55,810 So when a function is inside of a class 122 122 00:05:55,810 --> 00:05:57,460 it's called a method. 123 123 00:05:57,460 --> 00:06:00,420 So when you call the student class, 124 124 00:06:00,420 --> 00:06:02,030 notice that this bracket notation here 125 125 00:06:02,030 --> 00:06:03,950 is used to call a function normally. 126 126 00:06:03,950 --> 00:06:05,950 But we can also use it to call a class. 127 127 00:06:05,950 --> 00:06:08,430 When you call that Python will automatically 128 128 00:06:08,430 --> 00:06:12,610 call the init method for you and it will create 129 129 00:06:12,610 --> 00:06:16,720 this empty thing called self, and you will be able 130 130 00:06:16,720 --> 00:06:20,300 to modify the name property inside self 131 131 00:06:20,300 --> 00:06:22,080 and give it the value Rolf. 132 132 00:06:22,080 --> 00:06:24,550 The name property won't exist by default so doing 133 133 00:06:24,550 --> 00:06:26,990 this also creates it, which is quite nice. 134 134 00:06:26,990 --> 00:06:31,690 So once that's done and this self object contains 135 135 00:06:31,690 --> 00:06:36,690 a name property, Python will give you back that self. 136 136 00:06:37,930 --> 00:06:40,530 And student will become a name 137 137 00:06:40,530 --> 00:06:43,480 for the self thing we created, 138 138 00:06:43,480 --> 00:06:46,550 that thing being an object, that's what they're called. 139 139 00:06:46,550 --> 00:06:49,710 So we're using this class through the init method 140 140 00:06:49,710 --> 00:06:53,010 to create an object and assign the name property 141 141 00:06:53,010 --> 00:06:56,170 inside that object to the string Rolf. 142 142 00:06:56,170 --> 00:06:59,730 Then that object is what becomes the value 143 143 00:06:59,730 --> 00:07:01,920 for our student variable. 144 144 00:07:01,920 --> 00:07:05,590 So you can now do print student.name, 145 145 00:07:05,590 --> 00:07:07,320 and here what we're doing is we're accessing 146 146 00:07:07,320 --> 00:07:10,340 the name property of our student variable 147 147 00:07:10,340 --> 00:07:12,760 which as you know is the self 148 148 00:07:12,760 --> 00:07:17,580 that we created earlier on, so that will give you Rolf. 149 149 00:07:17,580 --> 00:07:21,940 And if I run that you see that Rolf comes out. 150 150 00:07:21,940 --> 00:07:25,940 This is how object oriented programming works in Python. 151 151 00:07:25,940 --> 00:07:29,220 You call a class, the init method runs, 152 152 00:07:29,220 --> 00:07:31,860 and what you get back is the object you created 153 153 00:07:31,860 --> 00:07:33,890 and in the init method you have the opportunity 154 154 00:07:33,890 --> 00:07:36,980 to set and change its properties. 155 155 00:07:36,980 --> 00:07:38,750 So what we've got here is the name property 156 156 00:07:38,750 --> 00:07:40,210 that we're changing. 157 157 00:07:40,210 --> 00:07:43,670 As well as self.name equals Rolf, we can do self.grades 158 158 00:07:43,670 --> 00:07:45,863 and make it equal to what we had before, 159 159 00:07:47,290 --> 00:07:48,123 something like that. 160 160 00:07:48,123 --> 00:07:51,270 So we're making the grades property of self 161 161 00:07:51,270 --> 00:07:52,670 equal to this tuple. 162 162 00:07:52,670 --> 00:07:54,720 And then when the function finishes, 163 163 00:07:54,720 --> 00:07:57,780 the class gives back self to student 164 164 00:07:57,780 --> 00:08:01,400 and now you can print out student.grades 165 165 00:08:01,400 --> 00:08:04,550 if you want and that property will exist there as well, 166 166 00:08:04,550 --> 00:08:05,383 as you can see. 167 167 00:08:06,800 --> 00:08:08,900 So nothing terribly complicated up til now. 168 168 00:08:08,900 --> 00:08:10,500 There's a bit of data being passed from 169 169 00:08:10,500 --> 00:08:11,760 one place to another, 170 170 00:08:11,760 --> 00:08:15,330 but this is no different to what we had before really. 171 171 00:08:15,330 --> 00:08:17,650 If you wanted to get the average of these grades 172 172 00:08:17,650 --> 00:08:21,150 you would still have to pass them to a function 173 173 00:08:21,150 --> 00:08:24,570 called average for example and that would give you 174 174 00:08:24,570 --> 00:08:26,840 the average if you had the function defined. 175 175 00:08:26,840 --> 00:08:28,890 But using object oriented programming, 176 176 00:08:28,890 --> 00:08:30,970 there's one more thing you can do which is going 177 177 00:08:30,970 --> 00:08:33,360 to simplify your life greatly, and that is the main 178 178 00:08:33,360 --> 00:08:35,047 point of object oriented programming, 179 179 00:08:35,047 --> 00:08:38,106 which is to define another method such as 180 180 00:08:38,106 --> 00:08:42,450 the average method inside the class. 181 181 00:08:42,450 --> 00:08:47,450 And this method will take self as a parameter. 182 182 00:08:48,515 --> 00:08:51,660 Notice that self again doesn't have to be self, 183 183 00:08:51,660 --> 00:08:53,140 you can call it whatever you want. 184 184 00:08:53,140 --> 00:08:55,360 That's just the convention in Python, 185 185 00:08:55,360 --> 00:08:56,830 we usually call it self but you can call it 186 186 00:08:56,830 --> 00:08:57,740 whatever you want. 187 187 00:08:57,740 --> 00:09:00,312 So if you define a method inside a class, 188 188 00:09:00,312 --> 00:09:04,680 all the methods inside the class have to take a parameter 189 189 00:09:04,680 --> 00:09:09,223 which will be the object that was created initially. 190 190 00:09:10,620 --> 00:09:14,810 You can do return sum of self.grades divided by len 191 191 00:09:14,810 --> 00:09:16,173 of self.grades. 192 192 00:09:17,090 --> 00:09:22,090 Notice how this method here does not take a sequence, 193 193 00:09:22,860 --> 00:09:27,170 it just uses the object that was created up here. 194 194 00:09:27,170 --> 00:09:31,758 So how does Python know that it needs to call 195 195 00:09:31,758 --> 00:09:35,200 this method with this data here. 196 196 00:09:35,200 --> 00:09:38,270 Well here's how it works internally. 197 197 00:09:38,270 --> 00:09:40,710 When you create a new class, the init method 198 198 00:09:40,710 --> 00:09:45,710 runs and you get this new object placed in student. 199 199 00:09:46,061 --> 00:09:51,061 Then whenever you want to call this method here, 200 200 00:09:51,270 --> 00:09:56,158 all you have to do is type out student, the class, 201 201 00:09:56,158 --> 00:10:01,158 dot average, and then of course because this is essentially 202 202 00:10:01,320 --> 00:10:06,133 another function, you put in there the student object. 203 203 00:10:07,128 --> 00:10:12,128 And what this is doing is it's hauling the average method 204 204 00:10:12,140 --> 00:10:13,740 inside, that's what the dot means, 205 205 00:10:13,740 --> 00:10:15,380 inside the student class, 206 206 00:10:15,380 --> 00:10:16,940 so that's this one there. 207 207 00:10:16,940 --> 00:10:19,970 And the self parameter is going to take the value 208 208 00:10:19,970 --> 00:10:23,360 of the student variable which has that object 209 209 00:10:23,360 --> 00:10:25,210 that was created earlier on that contains 210 210 00:10:25,210 --> 00:10:27,060 the name and the grades. 211 211 00:10:27,060 --> 00:10:29,420 So if we save that and run it, 212 212 00:10:29,420 --> 00:10:31,563 you can see that you get 88.2. 213 213 00:10:32,850 --> 00:10:35,910 Now this is a little bit verbose, there's a few 214 214 00:10:35,910 --> 00:10:37,770 too many words in there, so Python has a nice bit 215 215 00:10:37,770 --> 00:10:40,002 of syntax that you can use instead of this one 216 216 00:10:40,002 --> 00:10:43,960 which is to remove the student argument 217 217 00:10:43,960 --> 00:10:46,400 from the average function and instead of calling 218 218 00:10:46,400 --> 00:10:49,500 the average method inside the class, 219 219 00:10:49,500 --> 00:10:52,481 call it on the object itself. 220 220 00:10:52,481 --> 00:10:56,370 So if you do student.average, Python is going 221 221 00:10:56,370 --> 00:11:01,020 to realise that student is a student object, 222 222 00:11:01,020 --> 00:11:03,240 so you probably want to pass it as self, 223 223 00:11:03,240 --> 00:11:05,090 as the first argument. 224 224 00:11:05,090 --> 00:11:07,360 So it will do the conversion for you, 225 225 00:11:07,360 --> 00:11:10,200 that is the same thing and one is the other, 226 226 00:11:10,200 --> 00:11:11,380 but this is a little bit shorter, 227 227 00:11:11,380 --> 00:11:12,680 a little bit easier to read. 228 228 00:11:12,680 --> 00:11:15,830 And if you name your variables well, 229 229 00:11:15,830 --> 00:11:18,287 then this is pretty obvious what it's gonna give you back, 230 230 00:11:18,287 --> 00:11:20,860 it's gonna give you the average of this student. 231 231 00:11:20,860 --> 00:11:24,680 Now you can make it even better, type average grade say, 232 232 00:11:24,680 --> 00:11:26,190 and that's going to be just a little bit 233 233 00:11:26,190 --> 00:11:27,580 more readable as well. 234 234 00:11:27,580 --> 00:11:29,510 And just to show you that this works, 235 235 00:11:29,510 --> 00:11:31,210 it does exactly the same thing. 236 236 00:11:31,210 --> 00:11:34,070 So this is the key benefit of object oriented programming. 237 237 00:11:34,070 --> 00:11:36,960 You can define methods inside a class 238 238 00:11:36,960 --> 00:11:39,880 that use the object that was initially created 239 239 00:11:39,880 --> 00:11:42,631 by the init method within them. 240 240 00:11:42,631 --> 00:11:43,960 Show that and you don't have to keep track 241 241 00:11:43,960 --> 00:11:45,890 of multiple different pieces of data 242 242 00:11:45,890 --> 00:11:50,000 and the object itself can contain these methods 243 243 00:11:50,000 --> 00:11:51,190 that you want to use inside it, 244 244 00:11:51,190 --> 00:11:55,640 so all the data and the methods are in one place 245 245 00:11:55,640 --> 00:11:57,078 inside the class. 246 246 00:11:57,078 --> 00:12:00,260 Now the init method can also take arguments 247 247 00:12:00,260 --> 00:12:01,700 or have parameters. 248 248 00:12:01,700 --> 00:12:06,340 For example, we can have a name parameter as well as self, 249 249 00:12:06,340 --> 00:12:09,900 so just to recap, all methods inside a class 250 250 00:12:09,900 --> 00:12:14,408 need to have a parameter such as self 251 251 00:12:14,408 --> 00:12:16,711 so they can take in the object that 252 252 00:12:16,711 --> 00:12:19,210 you have been constructing. 253 253 00:12:19,210 --> 00:12:22,330 But they can also take more arguments, 254 254 00:12:22,330 --> 00:12:24,630 so here we're going to have another parameter, 255 255 00:12:24,630 --> 00:12:27,347 the name parameter, and then you'll put the value 256 256 00:12:27,347 --> 00:12:30,000 of that parameter in the bracket 257 257 00:12:30,000 --> 00:12:32,480 of the student class call. 258 258 00:12:32,480 --> 00:12:36,163 So we can put here Bob, let's say. 259 259 00:12:36,163 --> 00:12:40,150 So now Bob will become the value for name. 260 260 00:12:40,150 --> 00:12:43,060 Notice that self is given for you, so you don't have 261 261 00:12:43,060 --> 00:12:45,420 to give it a name, this here will become 262 262 00:12:45,420 --> 00:12:46,633 the value for name. 263 263 00:12:47,760 --> 00:12:52,570 But notice that we're not using this name parameter anyway. 264 264 00:12:52,570 --> 00:12:56,010 We are accessing here self.name, but that's the name 265 265 00:12:56,010 --> 00:13:00,410 property inside self, it is not this parameter. 266 266 00:13:00,410 --> 00:13:02,020 If you wanted to access this parameter, 267 267 00:13:02,020 --> 00:13:04,160 you can do that by doing something like that. 268 268 00:13:04,160 --> 00:13:06,850 Self.name which is the name property inside self 269 269 00:13:06,850 --> 00:13:10,320 will take the value of the name variable 270 270 00:13:10,320 --> 00:13:13,710 inside this method which is this parameter here. 271 271 00:13:13,710 --> 00:13:17,818 So now if you print student.name you'll see that Bob 272 272 00:13:17,818 --> 00:13:21,493 will come out because that is what we defined 273 273 00:13:21,493 --> 00:13:23,370 in the init method. 274 274 00:13:23,370 --> 00:13:25,033 Let's do the same with grades. 275 275 00:13:26,900 --> 00:13:29,356 And now as well as name, we have to pass in 276 276 00:13:29,356 --> 00:13:32,420 a set of grades for the student. 277 277 00:13:32,420 --> 00:13:35,800 For example, we will do this one, 278 278 00:13:35,800 --> 00:13:37,950 give it just a little bit of a different set 279 279 00:13:37,950 --> 00:13:41,030 of grades there, and now we can press play 280 280 00:13:41,030 --> 00:13:43,950 and notice how the average grade changes. 281 281 00:13:43,950 --> 00:13:46,680 The average grade is now being calculated 282 282 00:13:46,680 --> 00:13:50,029 from this set of grades because they are stored 283 283 00:13:50,029 --> 00:13:54,400 in self.grades for this student. 284 284 00:13:54,400 --> 00:13:56,550 So when the average grade method is called 285 285 00:13:56,550 --> 00:13:58,510 it uses those grades. 286 286 00:13:58,510 --> 00:14:02,550 Remember that you can define multiple students if you want 287 287 00:14:02,550 --> 00:14:04,120 and that's totally fine. 288 288 00:14:04,120 --> 00:14:07,730 This call here in line 10 will call the init method, 289 289 00:14:07,730 --> 00:14:09,965 it will give you a new object, it will populate 290 290 00:14:09,965 --> 00:14:14,965 self.name of that object with the name argument 291 291 00:14:15,110 --> 00:14:19,530 and self.grades of the self object with this argument. 292 292 00:14:19,530 --> 00:14:22,780 And it will give you this student variable back. 293 293 00:14:22,780 --> 00:14:24,980 I'm gonna call this student two. 294 294 00:14:24,980 --> 00:14:27,670 The student two variable, exactly the same thing, 295 295 00:14:27,670 --> 00:14:30,600 calls the init method, passes Rolf as the name 296 296 00:14:30,600 --> 00:14:33,100 and it creates a new object and sets the name 297 297 00:14:33,100 --> 00:14:35,440 property of that new object to Rolf 298 298 00:14:35,440 --> 00:14:37,270 and the grades property of that new object 299 299 00:14:37,270 --> 00:14:39,220 to this set of grades here. 300 300 00:14:39,220 --> 00:14:41,410 And what you end up with are two separate 301 301 00:14:41,410 --> 00:14:43,240 containers of data. 302 302 00:14:43,240 --> 00:14:46,330 The student variable which is Bob and has these grades, 303 303 00:14:46,330 --> 00:14:49,242 and the student two variable which is Rolf 304 304 00:14:49,242 --> 00:14:50,075 and has these grades. 305 305 00:14:50,075 --> 00:14:52,733 So when you call student2.average_grade, 306 306 00:14:55,240 --> 00:14:58,973 again what Python is doing is it's calling the student class 307 307 00:14:58,973 --> 00:15:01,923 and passing student to there. 308 308 00:15:02,850 --> 00:15:05,770 So self is student two. 309 309 00:15:05,770 --> 00:15:08,940 When you sum the grades you're going to be summing 310 310 00:15:08,940 --> 00:15:11,300 these grades here because those are the grades 311 311 00:15:11,300 --> 00:15:14,109 that are stored inside student two. 312 312 00:15:14,109 --> 00:15:17,880 But of course you can still do student2.average_grade 313 313 00:15:17,880 --> 00:15:19,783 instead as that is a bit simpler. 314 314 00:15:21,110 --> 00:15:24,600 Pressing play now will give you 92.2 and 88.2 315 315 00:15:24,600 --> 00:15:28,440 as the two averages, one for each student. 316 316 00:15:28,440 --> 00:15:29,760 All right, that's everything for this video. 317 317 00:15:29,760 --> 00:15:31,250 I wanted to tell you a little bit about 318 318 00:15:31,250 --> 00:15:33,880 how object oriented programming works in Python, 319 319 00:15:33,880 --> 00:15:36,786 how you can define classes, how objects are created, 320 320 00:15:36,786 --> 00:15:40,160 and how methods work so that you can call them 321 321 00:15:40,160 --> 00:15:43,030 with the data in those objects. 322 322 00:15:43,030 --> 00:15:44,930 I hope it's all clear, but if it isn't, 323 323 00:15:44,930 --> 00:15:47,245 please ask a question in the course Q and A, 324 324 00:15:47,245 --> 00:15:48,780 we'll be more than happy to help you out. 325 325 00:15:48,780 --> 00:15:50,090 Thanks for joining me in this video 326 326 00:15:50,090 --> 00:15:51,740 and I'll see you in the next one.