1 00:00:00,600 --> 00:00:01,560 Hey, welcome back. 2 00:00:01,589 --> 00:00:05,640 In this video, you learn how to create class variables. 3 00:00:05,640 --> 00:00:09,510 You have learned already how to create instance variables. 4 00:00:09,510 --> 00:00:12,880 So we have instance variables and we have class variables. 5 00:00:12,900 --> 00:00:18,570 I'll mention the difference between the two and show you what each of these are. 6 00:00:18,660 --> 00:00:27,480 We're going to work on the hotel booking app we've been building so far, but I'll simplify the main 7 00:00:27,720 --> 00:00:29,420 pie script a little bit. 8 00:00:29,430 --> 00:00:34,140 Actually, I'll just make a copy of this file, so please do the same. 9 00:00:34,470 --> 00:00:44,610 I'll name the second copy main to that P and then in main to that py, I'll simplify the code a little 10 00:00:44,610 --> 00:00:47,760 bit so I'll remove. 11 00:00:48,850 --> 00:00:53,350 The two classes, credit card and secure credit card. 12 00:00:54,490 --> 00:01:02,410 I'll remove the entire loop where we run the program, and I'll keep only the two classes, reservation 13 00:01:02,410 --> 00:01:04,450 ticket and hotel. 14 00:01:04,450 --> 00:01:09,520 And also these two lines are pointing to the cards that CSV file. 15 00:01:09,520 --> 00:01:11,560 So I'll remove those too. 16 00:01:11,590 --> 00:01:15,760 Now I'm also attaching this script to the lecture resources. 17 00:01:15,760 --> 00:01:21,010 So if you want to make sure that you have the same code as me, you can just copy that file and paste 18 00:01:21,010 --> 00:01:25,590 it in your project directory and name it with something like Main two PI. 19 00:01:25,810 --> 00:01:29,680 So instance variables versus class variables. 20 00:01:29,800 --> 00:01:33,800 You have already created instance variables. 21 00:01:33,820 --> 00:01:36,340 Instance variables are these. 22 00:01:37,530 --> 00:01:39,120 Hotel ID. 23 00:01:39,480 --> 00:01:47,530 Name for the hotel instances, customer name and hotel for the reservation. 24 00:01:47,550 --> 00:01:48,930 Ticket instances. 25 00:01:50,000 --> 00:01:56,750 Now let me create a class variable and then explain you the difference between a class variable and 26 00:01:56,750 --> 00:01:57,950 an instance variable. 27 00:01:58,430 --> 00:02:05,530 Class variables are coded outside the methods of a class instance. 28 00:02:05,540 --> 00:02:08,380 Variables are coded inside a method. 29 00:02:08,389 --> 00:02:10,520 Usually it's the init method. 30 00:02:11,190 --> 00:02:13,620 But class variables are coded here. 31 00:02:13,620 --> 00:02:23,610 For example, let's say watermark is equal to, let's say, the real estate company. 32 00:02:24,300 --> 00:02:28,860 This is the company that has this app, this hotel booking app. 33 00:02:28,860 --> 00:02:35,700 So they are a company who offer hotels for holidays for people who go to vacation and so on. 34 00:02:35,850 --> 00:02:43,130 So that means now this text is basically part of the class. 35 00:02:43,140 --> 00:02:48,690 It's not specific to a particular hotel, Right. 36 00:02:48,960 --> 00:02:51,130 That's why it is a class variable. 37 00:02:51,150 --> 00:02:57,450 Let me try to explain it better by creating some instances of the hotel class. 38 00:02:57,450 --> 00:03:02,100 So let's say hotel one is hotel ID is equal to. 39 00:03:02,370 --> 00:03:09,720 So this expects an ID actually its hotel ID, hotel ID is equal to. 40 00:03:09,870 --> 00:03:12,570 Well, let's give one of these IDs. 41 00:03:12,900 --> 00:03:17,400 Let's say 188 188. 42 00:03:18,980 --> 00:03:21,170 Let's create another a second instance. 43 00:03:21,170 --> 00:03:26,630 Hotel, two hotel, hotel ID that's equal to. 44 00:03:28,430 --> 00:03:29,810 134. 45 00:03:30,780 --> 00:03:39,640 Make sure to give them as strings because we are loading the ID field as a string here, the ID fields. 46 00:03:39,660 --> 00:03:42,390 These are read as strings inside Python. 47 00:03:42,870 --> 00:03:50,460 So 134 right now if I print out hotel one dot name. 48 00:03:52,770 --> 00:03:54,630 And I execute the script. 49 00:03:57,130 --> 00:03:59,890 I'll get Snow Palace, right. 50 00:03:59,920 --> 00:04:04,850 That's the value of the name instance variable. 51 00:04:04,870 --> 00:04:08,660 So this is a variable of this particular instance. 52 00:04:08,680 --> 00:04:12,970 And now if I do print hotel to that name. 53 00:04:15,420 --> 00:04:18,209 We'll get to sunny apartment. 54 00:04:18,720 --> 00:04:27,240 So because name gives us different values for different instances, that's why we call we call that 55 00:04:27,240 --> 00:04:29,430 variable an instance variable. 56 00:04:29,430 --> 00:04:30,100 Right. 57 00:04:30,120 --> 00:04:36,720 But now, if you do print hotel one dot watermark. 58 00:04:39,370 --> 00:04:40,720 And we do the same. 59 00:04:40,750 --> 00:04:44,050 Let me duplicate this with control D or command D. 60 00:04:44,320 --> 00:04:46,510 So let's do hotel to that watermark. 61 00:04:46,540 --> 00:04:51,910 You'll see that, of course, we'll get the same value for both of these print functions. 62 00:04:52,390 --> 00:05:01,120 So that makes Watermark a class variable because the value of the variable is shared among all instances. 63 00:05:01,120 --> 00:05:10,630 Plus you can also access that's variable using hotel dot watermark. 64 00:05:12,710 --> 00:05:18,700 Execute and you will see that we get three lines printed out. 65 00:05:18,710 --> 00:05:21,710 So hotel is the name of the class. 66 00:05:21,830 --> 00:05:25,160 So Watermark belongs to that class. 67 00:05:27,500 --> 00:05:33,290 If we do print hotel dot name, you're going to get an error. 68 00:05:35,880 --> 00:05:36,780 So here we go. 69 00:05:36,810 --> 00:05:43,860 Hotel has no attribute name because name is an attribute of the instances. 70 00:05:44,520 --> 00:05:51,120 Now, what's what's the benefit of having a class variable, and when should you have a class variable? 71 00:05:51,270 --> 00:06:00,420 Well, the benefit is that the value of that variable can be shared across all the instances as you 72 00:06:00,420 --> 00:06:01,140 saw. 73 00:06:01,320 --> 00:06:03,390 So that means. 74 00:06:04,400 --> 00:06:13,970 If you think that all the instances should have access to one same value as is the case here. 75 00:06:13,970 --> 00:06:19,130 So all these hotels are part of this real estate company. 76 00:06:19,130 --> 00:06:28,550 So the company perhaps they want to print out that watermark, that label somewhere in the tickets or 77 00:06:28,550 --> 00:06:29,450 anywhere. 78 00:06:29,750 --> 00:06:36,740 So if you have an HTML frontend, for example, you have a web app and you want to display that label 79 00:06:36,740 --> 00:06:46,040 on the web app, then you could get that label from the hotel class like we did here or from the hotel 80 00:06:46,040 --> 00:06:48,410 instance, depending on the scenario. 81 00:06:48,770 --> 00:06:54,320 So that's the difference between instance variables and class variables. 82 00:06:54,530 --> 00:06:56,360 So self is a variable. 83 00:06:56,360 --> 00:07:04,280 In the case of Hotel one, it holds the hotel one instance in the case of hotel two, self holds the 84 00:07:04,280 --> 00:07:05,570 hotel to instance. 85 00:07:06,340 --> 00:07:09,230 And then you get name out of self or watermark. 86 00:07:09,250 --> 00:07:15,130 So self has access to both the watermark and hotel ID and name and so on. 87 00:07:15,440 --> 00:07:16,780 Yeah, I hope that's clear. 88 00:07:16,780 --> 00:07:21,340 And in the next video we'll cover instance methods versus class methods. 89 00:07:21,370 --> 00:07:22,060 I'll see you there.