1 1 00:00:00,120 --> 00:00:01,690 Hi guys and welcome back, 2 2 00:00:01,690 --> 00:00:04,670 in this video we're going to learn about two methods, 3 3 00:00:04,670 --> 00:00:07,870 the str and the repr methods. 4 4 00:00:07,870 --> 00:00:10,660 In Python methods with two underscores on each side 5 5 00:00:10,660 --> 00:00:13,920 are special methods also called magic methods at times, 6 6 00:00:13,920 --> 00:00:17,950 because Python will call them for you in some situations. 7 7 00:00:17,950 --> 00:00:20,540 For example when you do person, 8 8 00:00:20,540 --> 00:00:22,400 Python calls the init method for you, 9 9 00:00:22,400 --> 00:00:23,560 even though you didn't say 10 10 00:00:23,560 --> 00:00:26,810 Python dot underscore, underscore init, you know. 11 11 00:00:26,810 --> 00:00:28,700 So that is why it is a magic method, 12 12 00:00:28,700 --> 00:00:30,930 you don't have to call it yourself, 13 13 00:00:30,930 --> 00:00:33,540 Python can do it for you at times. 14 14 00:00:33,540 --> 00:00:38,540 So let's create a person that I'm gonna call Bob here 15 15 00:00:39,000 --> 00:00:41,150 and he's gonna be 35. 16 16 00:00:41,150 --> 00:00:46,040 Here we're creating a person object by calling the class, 17 17 00:00:46,040 --> 00:00:48,720 then Python calls the underscore, underscore, 18 18 00:00:48,720 --> 00:00:50,420 init, underscore, underscore method. 19 19 00:00:50,420 --> 00:00:54,680 Gives us a new empty object that we're calling self, 20 20 00:00:54,680 --> 00:00:55,940 and then we're setting the name 21 21 00:00:55,940 --> 00:00:59,690 and the age properties of that object to be our parameters 22 22 00:00:59,690 --> 00:01:01,600 that are arguments here, 23 23 00:01:01,600 --> 00:01:06,600 so Bob and 35 will be stored in Bob's name and age. 24 24 00:01:07,150 --> 00:01:10,950 Now if we print Bob then you may see something 25 25 00:01:10,950 --> 00:01:14,030 a little bit weird, which is this. 26 26 00:01:14,030 --> 00:01:17,030 That's less than, underscore, underscore, main, 27 27 00:01:17,030 --> 00:01:18,840 underscore, underscore, dot, person, 28 28 00:01:18,840 --> 00:01:22,240 object, at, a bunch of numbers. 29 29 00:01:22,240 --> 00:01:23,073 Greater than. 30 30 00:01:23,073 --> 00:01:24,360 So what does this mean? 31 31 00:01:24,360 --> 00:01:26,480 What python is doing at this point is 32 32 00:01:26,480 --> 00:01:28,210 when you've told it to print Bob, 33 33 00:01:28,210 --> 00:01:32,050 Python is going to print out a string 34 34 00:01:32,050 --> 00:01:35,740 representing the Bob objects that we've created. 35 35 00:01:35,740 --> 00:01:38,030 And the reason why Python is printing out 36 36 00:01:38,030 --> 00:01:39,930 a representation of the object, 37 37 00:01:39,930 --> 00:01:42,270 is because you can't really print an object, 38 38 00:01:42,270 --> 00:01:44,980 you have to print a string, some characters 39 39 00:01:44,980 --> 00:01:46,430 and numbers and so on. 40 40 00:01:46,430 --> 00:01:49,940 So Python is saying that this string 41 41 00:01:49,940 --> 00:01:54,790 that it printed out is what it thinks represents our object, 42 42 00:01:54,790 --> 00:01:57,370 this is a default string, and all objects 43 43 00:01:57,370 --> 00:02:01,090 and all classes you create will look something like that, 44 44 00:02:01,090 --> 00:02:03,110 unless you change it yourself. 45 45 00:02:03,110 --> 00:02:07,720 So the purpose of printing out an object can be to fold. 46 46 00:02:07,720 --> 00:02:10,390 The first purpose can be to return 47 47 00:02:10,390 --> 00:02:14,700 a nice, easy to read string so that in your applications 48 48 00:02:14,700 --> 00:02:16,270 you can print out an object 49 49 00:02:16,270 --> 00:02:18,850 and your users can make use of that. 50 50 00:02:18,850 --> 00:02:22,850 For example if they wanted to know about this Bob person 51 51 00:02:22,850 --> 00:02:25,040 then potentially you could print out Bob 52 52 00:02:25,040 --> 00:02:27,420 and it could show them some nice information about Bob. 53 53 00:02:27,420 --> 00:02:29,840 The other reason to print out an object 54 54 00:02:29,840 --> 00:02:33,610 can be for programmers, you can print out an object 55 55 00:02:33,610 --> 00:02:35,850 so that you can see the objects information 56 56 00:02:35,850 --> 00:02:38,570 in case you want to recreate the object. 57 57 00:02:38,570 --> 00:02:40,360 Let's start off with the first option. 58 58 00:02:40,360 --> 00:02:44,880 We're going to modify Bob so that when we print him out 59 59 00:02:44,880 --> 00:02:46,880 we'll get some nice information 60 60 00:02:46,880 --> 00:02:50,180 that our users can make use of. 61 61 00:02:50,180 --> 00:02:54,800 The way we do that is we do def, underscore, underscore, 62 62 00:02:54,800 --> 00:02:57,490 str, underscore, underscore. 63 63 00:02:57,490 --> 00:03:00,230 Then of course the self parameter, 64 64 00:03:00,230 --> 00:03:03,250 and in we go to the Bobby. 65 65 00:03:03,250 --> 00:03:05,640 The underscore, underscore, str, underscore, underscore 66 66 00:03:05,640 --> 00:03:08,060 is a method, that is a magic method 67 67 00:03:08,060 --> 00:03:10,260 because it has the two underscores on each side, 68 68 00:03:10,260 --> 00:03:12,860 and this method gets called for you, 69 69 00:03:12,860 --> 00:03:16,600 when you want to turn your object into a string. 70 70 00:03:16,600 --> 00:03:18,977 Let me just return hello from here. 71 71 00:03:18,977 --> 00:03:21,093 Any now we're going to print Bob. 72 72 00:03:22,160 --> 00:03:24,650 Notice that we get hello out. 73 73 00:03:24,650 --> 00:03:25,979 Because what Python has done, 74 74 00:03:25,979 --> 00:03:28,840 is when you ask it to print an object, 75 75 00:03:28,840 --> 00:03:30,810 Python realises that really what you want 76 76 00:03:30,810 --> 00:03:33,520 is a string representation of that object since 77 77 00:03:33,520 --> 00:03:34,700 that's the only thing you can actually 78 78 00:03:34,700 --> 00:03:36,090 print out in a console. 79 79 00:03:36,090 --> 00:03:38,580 When you ask it to print an object it is going to 80 80 00:03:38,580 --> 00:03:42,910 turn that object into a string using the str method, 81 81 00:03:42,910 --> 00:03:44,830 and then it's going to print that. 82 82 00:03:44,830 --> 00:03:47,000 So instead of returning hello here, 83 83 00:03:47,000 --> 00:03:49,220 we could return something a bit nicer. 84 84 00:03:49,220 --> 00:03:51,950 Run about the goal, remember the goal 85 85 00:03:51,950 --> 00:03:53,860 when you're using the underscore, underscore, 86 86 00:03:53,860 --> 00:03:56,160 str, underscore, underscore method is to 87 87 00:03:56,160 --> 00:04:01,160 print out a nice, easy to read string for users. 88 88 00:04:01,360 --> 00:04:04,570 So we're going to print something like this, 89 89 00:04:04,570 --> 00:04:09,570 person, self, dot name, self dot age, years old. 90 90 00:04:10,660 --> 00:04:12,980 Now if we run this code again, 91 91 00:04:12,980 --> 00:04:16,260 you see that we get person Bob, 35 years old. 92 92 00:04:16,260 --> 00:04:18,130 You can remove the person if you'd like. 93 93 00:04:18,130 --> 00:04:22,400 So as well as the str method, you have another one 94 94 00:04:22,400 --> 00:04:25,490 called the repr method. 95 95 00:04:25,490 --> 00:04:28,960 The goal of the repr method is to be unambiguous, 96 96 00:04:28,960 --> 00:04:31,888 and if possible it should return a string 97 97 00:04:31,888 --> 00:04:36,600 that allows us to recreate the original object very easily. 98 98 00:04:36,600 --> 00:04:41,600 So I'm going to return person, self dot name, self dot age. 99 99 00:04:42,540 --> 00:04:43,373 Like that. 100 100 00:04:43,373 --> 00:04:45,450 Notice that I'm putting less than and greater than symbols 101 101 00:04:45,450 --> 00:04:48,970 that is just for looks, it is to tell programmers 102 102 00:04:48,970 --> 00:04:50,730 that read this string here 103 103 00:04:50,730 --> 00:04:53,060 that we are printing out an object. 104 104 00:04:53,060 --> 00:04:55,500 Now if we press play, you can see 105 105 00:04:55,500 --> 00:04:59,260 that the str methods output is still printed out. 106 106 00:04:59,260 --> 00:05:02,690 That is because by default when you print out an object 107 107 00:05:02,690 --> 00:05:05,840 Python assumes that you wanna show it to your users. 108 108 00:05:05,840 --> 00:05:08,100 You don't want to show the output of the repr method, 109 109 00:05:08,100 --> 00:05:10,840 you wanna show the output of the str method. 110 110 00:05:10,840 --> 00:05:13,800 The repr method is used in a few other places 111 111 00:05:13,800 --> 00:05:15,520 such as the Python debugger 112 112 00:05:15,520 --> 00:05:17,381 that we will learn about later on. 113 113 00:05:17,381 --> 00:05:19,362 But usually the str method is used 114 114 00:05:19,362 --> 00:05:23,010 so if you wanna make sure to test out your repr method, 115 115 00:05:23,010 --> 00:05:24,240 just comment this one out, 116 116 00:05:24,240 --> 00:05:26,370 put a couple of hash symbols in front of it 117 117 00:05:26,370 --> 00:05:27,700 and then press play. 118 118 00:05:27,700 --> 00:05:31,980 And then you see that you get person, Bob, 35. 119 119 00:05:31,980 --> 00:05:35,530 And if you really wanted to you can put the quotes in there, 120 120 00:05:35,530 --> 00:05:38,950 so that when you press play you out string back, 121 121 00:05:38,950 --> 00:05:39,990 that's even better. 122 122 00:05:39,990 --> 00:05:41,680 So we've learned about two methods, 123 123 00:05:41,680 --> 00:05:44,210 that you can implement in your classes, 124 124 00:05:44,210 --> 00:05:47,230 the str and the repr methods. 125 125 00:05:47,230 --> 00:05:49,400 The str method is called when you wanna 126 126 00:05:49,400 --> 00:05:51,650 turn your object into a string 127 127 00:05:51,650 --> 00:05:52,780 such as when printing it out 128 128 00:05:52,780 --> 00:05:55,790 or even when doing str of Bob 129 129 00:05:55,790 --> 00:05:57,870 as we have learned previously with integers. 130 130 00:05:57,870 --> 00:06:00,280 The repr method is used to print out 131 131 00:06:00,280 --> 00:06:02,870 an unambiguous representation of an abject 132 132 00:06:02,870 --> 00:06:05,920 so that you can use that to recreate the object for example, 133 133 00:06:05,920 --> 00:06:09,330 if you were a programmer looking at that output. 134 134 00:06:09,330 --> 00:06:11,780 Usually you'll want to implement the str method, 135 135 00:06:11,780 --> 00:06:14,980 but implementing the repr method can also be quite nice. 136 136 00:06:14,980 --> 00:06:17,140 And remember you don't have to use these two, 137 137 00:06:17,140 --> 00:06:20,070 they're only used for representing an object 138 138 00:06:20,070 --> 00:06:22,130 as a string but you don't have to do that, 139 139 00:06:22,130 --> 00:06:23,180 if you don't want. 140 140 00:06:23,180 --> 00:06:24,100 That's it for this video, 141 141 00:06:24,100 --> 00:06:26,250 thank you for joining me and i'll see you--