1 1 00:00:01,970 --> 00:00:03,550 Hi guys, welcome back. 2 2 00:00:03,550 --> 00:00:06,060 In this video we're going to be adding dataclasses 3 3 00:00:06,060 --> 00:00:07,570 to our project. 4 4 00:00:07,570 --> 00:00:10,130 So we're back with a pricing service project 5 5 00:00:10,130 --> 00:00:13,105 and at the alert model. 6 6 00:00:13,105 --> 00:00:15,420 And we're gonna be taking this init method 7 7 00:00:15,420 --> 00:00:19,077 and turning it into its dataclass equivalent. 8 8 00:00:19,077 --> 00:00:20,430 And remember what that's gonna do, 9 9 00:00:20,430 --> 00:00:22,990 it is going to allow us to compare alerts 10 10 00:00:22,990 --> 00:00:25,210 and also represent them as strings 11 11 00:00:25,210 --> 00:00:28,140 when we print them out much more effectively. 12 12 00:00:28,140 --> 00:00:30,870 That's particularly helpful for when you're debugging 13 13 00:00:30,870 --> 00:00:33,600 and you can see the alert with more information 14 14 00:00:33,600 --> 00:00:35,650 without having to drill down into it. 15 15 00:00:35,650 --> 00:00:36,790 You'll know what I mean 16 16 00:00:36,790 --> 00:00:39,073 as we start debugging this project later on. 17 17 00:00:40,330 --> 00:00:43,870 For now though, we're going to go ahead and import 18 18 00:00:43,870 --> 00:00:44,793 the dataclasses. 19 19 00:00:49,110 --> 00:00:51,750 And we're gonna apply the dataclass decorator 20 20 00:00:51,750 --> 00:00:54,633 into this alert. 21 21 00:00:55,490 --> 00:00:58,750 Now at this decorator, you can pass in 22 22 00:00:58,750 --> 00:01:02,200 some configuration properties if you want as well. 23 23 00:01:02,200 --> 00:01:05,490 For example, you can say init equal false 24 24 00:01:05,490 --> 00:01:08,773 if you don't want an init method to be generated for you. 25 25 00:01:09,720 --> 00:01:11,240 And you can pass in a bunch of more things 26 26 00:01:11,240 --> 00:01:12,720 and I'm gonna link the documentation 27 27 00:01:12,720 --> 00:01:14,800 in the resources section so you can have a look 28 28 00:01:14,800 --> 00:01:17,390 at everything that you can do with dataclasses. 29 29 00:01:17,390 --> 00:01:21,763 But for now, what I'm going to do is eq equal false. 30 30 00:01:22,660 --> 00:01:25,050 And what this is gonna do is it's going to remove 31 31 00:01:25,050 --> 00:01:28,800 all equality generation from our dataclass. 32 32 00:01:28,800 --> 00:01:30,480 So what I said earlier about us being able 33 33 00:01:30,480 --> 00:01:33,190 to compare alerts with the dataclasses, 34 34 00:01:33,190 --> 00:01:35,430 we're gonna take that away from the dataclass. 35 35 00:01:35,430 --> 00:01:38,190 So now we will no longer be able to compare alerts. 36 36 00:01:38,190 --> 00:01:40,030 Why are doing that? 37 37 00:01:40,030 --> 00:01:42,370 Well, it doesn't really make sense for us 38 38 00:01:42,370 --> 00:01:45,420 to compare two alerts in our application. 39 39 00:01:45,420 --> 00:01:49,500 So in order to prevent us from accidentally doing that 40 40 00:01:49,500 --> 00:01:53,040 we take that away and those methods won't be generated 41 41 00:01:53,040 --> 00:01:55,110 and instead when we try to compare two alerts, 42 42 00:01:55,110 --> 00:01:56,540 we'll get an error saying, 43 43 00:01:56,540 --> 00:01:58,060 these two objects are not comparable 44 44 00:01:58,060 --> 00:02:00,520 because you don't have a way of comparing them. 45 45 00:02:00,520 --> 00:02:02,320 So that's why I'm making that false. 46 46 00:02:03,450 --> 00:02:06,380 Next thing is, we're gonna take this collection string 47 47 00:02:06,380 --> 00:02:08,990 and we're gonna turn it into a dataclass. 48 48 00:02:08,990 --> 00:02:11,070 The way we do that is we first of all have to say 49 49 00:02:11,070 --> 00:02:12,580 what type it is, it's a string, 50 50 00:02:12,580 --> 00:02:14,440 and then we're gonna say it's a field, 51 51 00:02:14,440 --> 00:02:17,290 it's not going to be included in the init method 52 52 00:02:17,290 --> 00:02:19,453 and the default is going to be alerts. 53 53 00:02:20,490 --> 00:02:22,060 So what does this do, 54 54 00:02:22,060 --> 00:02:25,360 well it tells a dataclass about this collection 55 55 00:02:25,360 --> 00:02:29,240 because it is now defined in the proper dataclass format 56 56 00:02:29,240 --> 00:02:31,460 and we've got it as a field. 57 57 00:02:31,460 --> 00:02:33,530 It's not going to be included in the init method 58 58 00:02:33,530 --> 00:02:35,310 which means it cannot be modified 59 59 00:02:35,310 --> 00:02:37,430 when we create a new object 60 60 00:02:37,430 --> 00:02:39,420 and the default is going to be alerts 61 61 00:02:39,420 --> 00:02:41,230 and because it can't be modified 62 62 00:02:41,230 --> 00:02:43,173 that is gonna be the value it has. 63 63 00:02:44,570 --> 00:02:47,333 So we can now take it away from there. 64 64 00:02:49,770 --> 00:02:54,290 Next we've got item id, price limit and underscore id. 65 65 00:02:54,290 --> 00:02:57,510 So, item id is just a string 66 66 00:02:57,510 --> 00:02:59,590 and it's passed into the init method you know 67 67 00:02:59,590 --> 00:03:01,830 and that's fine. 68 68 00:03:01,830 --> 00:03:06,510 Then we've got price limit which is here a float, 69 69 00:03:06,510 --> 00:03:09,343 so we're gonna have to say that it's gonna be a float. 70 70 00:03:10,410 --> 00:03:12,270 And then we've got underscore id 71 71 00:03:12,270 --> 00:03:15,203 which is gonna be a string. 72 72 00:03:17,140 --> 00:03:18,860 And once again it's gonna be field 73 73 00:03:18,860 --> 00:03:20,310 and it's gonna have a default factory 74 74 00:03:20,310 --> 00:03:24,253 of lambda uuid uuid4 hex, as we've seen before. 75 75 00:03:25,090 --> 00:03:28,320 So that takes care of this item id, 76 76 00:03:28,320 --> 00:03:31,560 this price limit and this underscore id. 77 77 00:03:31,560 --> 00:03:33,830 What else do we have to do? 78 78 00:03:33,830 --> 00:03:36,030 Do we have to tell the dataclass anything 79 79 00:03:36,030 --> 00:03:38,660 about the superclass? 80 80 00:03:38,660 --> 00:03:42,630 Should the superclass also be a dataclass? 81 81 00:03:42,630 --> 00:03:44,530 And the answer is no to both of those. 82 82 00:03:45,460 --> 00:03:47,340 If there is a superclass, 83 83 00:03:47,340 --> 00:03:49,570 the dataclass generated init method 84 84 00:03:49,570 --> 00:03:52,040 will call the init method of the superclass for you 85 85 00:03:52,040 --> 00:03:54,320 so you don't have to worry about it. 86 86 00:03:54,320 --> 00:03:58,010 And the superclasses don't have to be dataclasses. 87 87 00:03:58,010 --> 00:04:01,350 So just a normal class works fine, 88 88 00:04:01,350 --> 00:04:04,730 the dataclass is only for generating 89 89 00:04:04,730 --> 00:04:06,480 the code that it generates. 90 90 00:04:06,480 --> 00:04:10,010 Init method, repr methods, comparisons, hashing 91 91 00:04:10,010 --> 00:04:11,410 that sort of stuff. 92 92 00:04:11,410 --> 00:04:14,240 The superclass doesn't have to be a dataclass. 93 93 00:04:14,240 --> 00:04:16,420 But we do have a final thing 94 94 00:04:16,420 --> 00:04:20,100 that this dataclass does not take care of, 95 95 00:04:20,100 --> 00:04:22,763 and that is self.item. 96 96 00:04:23,810 --> 00:04:27,620 Self.item is not passed in as a parameter 97 97 00:04:27,620 --> 00:04:32,080 and it is also not generated as a standalone function. 98 98 00:04:32,080 --> 00:04:34,540 Notice that these default factories 99 99 00:04:34,540 --> 00:04:38,370 can generate a value but they cannot access 100 100 00:04:38,370 --> 00:04:41,383 other values that are passed in to the dataclass. 101 101 00:04:42,550 --> 00:04:47,320 So there is seemingly, no way for us to do this. 102 102 00:04:47,320 --> 00:04:48,930 Which is precisely why, 103 103 00:04:48,930 --> 00:04:50,410 when you're working with dataclasses, 104 104 00:04:50,410 --> 00:04:53,320 you do have an extra dunder method 105 105 00:04:53,320 --> 00:04:55,923 which is dunder post init. 106 106 00:04:57,030 --> 00:05:02,030 The post init method will run after the init method 107 107 00:05:03,440 --> 00:05:05,430 and it has access to self. 108 108 00:05:05,430 --> 00:05:09,500 So when this method runs directly after the init, 109 109 00:05:09,500 --> 00:05:13,070 you've already got these values stored in self 110 110 00:05:13,070 --> 00:05:18,070 which means you can do self.item equal item.get by id 111 111 00:05:18,160 --> 00:05:19,793 with self.item id. 112 112 00:05:21,810 --> 00:05:24,837 Now we've got this turned into a dataclass. 113 113 00:05:25,920 --> 00:05:28,000 And it works exactly the same way as we had before, 114 114 00:05:28,000 --> 00:05:29,860 no difference. 115 115 00:05:29,860 --> 00:05:32,100 Next let's move on to item.py 116 116 00:05:32,100 --> 00:05:33,950 and we're gonna do something similar. 117 117 00:05:35,000 --> 00:05:40,000 Okay, for the collection we're going to do this, 118 118 00:05:40,100 --> 00:05:44,040 as we know and then we've got URL, tag name, query 119 119 00:05:44,040 --> 00:05:45,500 and underscore id. 120 120 00:05:45,500 --> 00:05:47,980 So that's URL is just a string. 121 121 00:05:47,980 --> 00:05:50,050 Tag name is just a string. 122 122 00:05:50,050 --> 00:05:52,070 Query is a Dict. 123 123 00:05:52,070 --> 00:05:55,030 And underscore id is a string 124 124 00:05:56,240 --> 00:06:00,573 with a default factory of lambda uuid uuid4 hex. 125 125 00:06:02,070 --> 00:06:06,020 We do have to apply the dataclass decorator here 126 126 00:06:06,020 --> 00:06:08,290 and once again I'm gonna say, eq equal false 127 127 00:06:08,290 --> 00:06:11,360 so that we can't compare two items. 128 128 00:06:11,360 --> 00:06:12,480 And that's it. 129 129 00:06:12,480 --> 00:06:14,900 And we also don't need this repr method here 130 130 00:06:14,900 --> 00:06:18,210 because the dataclass is gonna generate it for us. 131 131 00:06:18,210 --> 00:06:21,320 There is one more thing which is the self.price. 132 132 00:06:21,320 --> 00:06:24,150 Self.price is set to none 133 133 00:06:24,150 --> 00:06:28,010 in this item model, in the init method. 134 134 00:06:28,010 --> 00:06:30,513 But it is not defined in our dataclass. 135 135 00:06:32,150 --> 00:06:34,910 So once again, and just for now, 136 136 00:06:34,910 --> 00:06:37,500 we're going to keep a post init here 137 137 00:06:37,500 --> 00:06:40,763 just to define the price as none. 138 138 00:06:41,980 --> 00:06:43,340 Okay? 139 139 00:06:43,340 --> 00:06:47,173 That is so that you can still access this self.price here. 140 140 00:06:48,690 --> 00:06:51,090 Now it says that the instance attribute price 141 141 00:06:51,090 --> 00:06:53,910 is defined outside the init, and it's not wrong. 142 142 00:06:53,910 --> 00:06:56,000 It is defined inside the post init 143 143 00:06:56,000 --> 00:06:57,070 but you can be sure 144 144 00:06:57,070 --> 00:06:59,780 that this going to be called directly after init. 145 145 00:06:59,780 --> 00:07:01,260 So there's nothing to worry about 146 146 00:07:01,260 --> 00:07:02,710 and soon in just a few videos, 147 147 00:07:02,710 --> 00:07:05,320 we're actually going to move it over up here. 148 148 00:07:05,320 --> 00:07:07,993 So don't worry too much about this for just now. 149 149 00:07:10,180 --> 00:07:12,030 Finally, we'll go over to store 150 150 00:07:12,030 --> 00:07:14,993 and we'll do something more or less similar. 151 151 00:07:18,850 --> 00:07:20,680 We'll start with the collection 152 152 00:07:20,680 --> 00:07:23,260 and then we've got name, URL prefix, 153 153 00:07:23,260 --> 00:07:26,057 tag name, query and underscore id. 154 154 00:07:26,057 --> 00:07:27,670 And this one's very straightforward 155 155 00:07:27,670 --> 00:07:29,080 because there's nothing else 156 156 00:07:29,080 --> 00:07:30,700 other than these name equal name, 157 157 00:07:30,700 --> 00:07:33,490 URL prefix equal URL prefix and so on. 158 158 00:07:33,490 --> 00:07:35,493 So all we have to do is say name, 159 159 00:07:36,560 --> 00:07:37,573 URL prefix, 160 160 00:07:39,090 --> 00:07:39,983 tag name, 161 161 00:07:40,830 --> 00:07:42,420 query, 162 162 00:07:42,420 --> 00:07:43,703 and underscore id. 163 163 00:07:47,930 --> 00:07:48,763 Like that. 164 164 00:07:48,763 --> 00:07:50,680 And we can take this whole thing away. 165 165 00:07:50,680 --> 00:07:52,420 That's all the changes we have to make 166 166 00:07:52,420 --> 00:07:54,400 in order to turn our code 167 167 00:07:54,400 --> 00:07:59,020 from using old style normal classes I guess, 168 168 00:07:59,020 --> 00:08:00,700 into dataclasses. 169 169 00:08:00,700 --> 00:08:03,390 Now, there is no reason why you should aim 170 170 00:08:03,390 --> 00:08:06,250 to use dataclasses everywhere. 171 171 00:08:06,250 --> 00:08:08,363 But, there are a few benefits. 172 172 00:08:09,320 --> 00:08:11,080 The code it generates, 173 173 00:08:11,080 --> 00:08:12,870 is usually going to be better than the code 174 174 00:08:12,870 --> 00:08:14,570 we would write ourselves. 175 175 00:08:14,570 --> 00:08:17,630 Just because it has been very carefully crafted 176 176 00:08:17,630 --> 00:08:19,120 so that it is efficient. 177 177 00:08:19,120 --> 00:08:21,080 So that it gives you the information you need. 178 178 00:08:21,080 --> 00:08:23,790 So that it checks for errors and things like that 179 179 00:08:23,790 --> 00:08:26,840 that you may not otherwise check for. 180 180 00:08:26,840 --> 00:08:30,430 And also there is probably the most important reason 181 181 00:08:30,430 --> 00:08:33,970 for me at least, it is a bit more readable. 182 182 00:08:33,970 --> 00:08:36,940 You define what things this object is going to have 183 183 00:08:36,940 --> 00:08:38,090 at the top of the file. 184 184 00:08:38,990 --> 00:08:42,830 And then everything is generated for you using these. 185 185 00:08:42,830 --> 00:08:44,890 There's no separate information, 186 186 00:08:44,890 --> 00:08:47,460 there's no potential chance to forget, 187 187 00:08:47,460 --> 00:08:50,210 to put something in the init method or to add a parameter 188 188 00:08:50,210 --> 00:08:51,370 or something like that. 189 189 00:08:51,370 --> 00:08:53,030 Everything's here. 190 190 00:08:53,030 --> 00:08:54,780 If it doesn't have init false, 191 191 00:08:54,780 --> 00:08:56,380 it's included in the init method 192 192 00:08:57,410 --> 00:09:01,560 and yeah, you can just see everything in the one place. 193 193 00:09:01,560 --> 00:09:03,850 The code that is generated is good, 194 194 00:09:03,850 --> 00:09:07,340 at least in my opinion, you should check this out yourself 195 195 00:09:07,340 --> 00:09:10,870 by looking at the talk that was linked in the last video. 196 196 00:09:10,870 --> 00:09:14,140 And I am happy that this is an improvement 197 197 00:09:14,140 --> 00:09:15,713 over the previous code. 198 198 00:09:16,950 --> 00:09:18,970 So, we are ready to move on. 199 199 00:09:18,970 --> 00:09:23,750 This is better code, we can continue with our application. 200 200 00:09:23,750 --> 00:09:26,450 Thanks for joining me, I'll see you in the next video.