1 1 00:00:01,380 --> 00:00:02,670 Hey guys, welcome back. 2 2 00:00:02,670 --> 00:00:04,370 In this video, we're going to start 3 3 00:00:04,370 --> 00:00:06,940 working on our item model. 4 4 00:00:06,940 --> 00:00:09,420 A model, as we discussed earlier on, 5 5 00:00:09,420 --> 00:00:13,840 is something that our application deals with internally. 6 6 00:00:13,840 --> 00:00:16,820 So whenever we want to use 7 7 00:00:16,820 --> 00:00:18,830 a thing in our programme 8 8 00:00:18,830 --> 00:00:21,280 and we want to be able to think of that thing 9 9 00:00:21,280 --> 00:00:23,570 as if it were something in the real world, 10 10 00:00:23,570 --> 00:00:25,833 we often will wanna create a model for it. 11 11 00:00:26,920 --> 00:00:29,430 For example, our application will have a model, 12 12 00:00:29,430 --> 00:00:33,440 which is the item, item that belongs to a store 13 13 00:00:33,440 --> 00:00:37,410 and that you can get a price of and things like that. 14 14 00:00:37,410 --> 00:00:40,810 So all of those interactions that we can do with an item, 15 15 00:00:40,810 --> 00:00:44,850 thing in the real world, like check where it is sold 16 16 00:00:44,850 --> 00:00:48,920 or find out what price it is or get its name, 17 17 00:00:48,920 --> 00:00:52,390 all those sort of things we can put into our item model. 18 18 00:00:52,390 --> 00:00:54,500 So we're going to go ahead and create that 19 19 00:00:54,500 --> 00:00:58,020 by going into Models and then right-click it 20 20 00:00:58,020 --> 00:01:01,090 and go to New Python file 21 21 00:01:01,090 --> 00:01:03,890 and we're gonna create one called Item. 22 22 00:01:03,890 --> 00:01:06,513 Now, before we get into coding the item, 23 23 00:01:07,580 --> 00:01:11,040 you have to think about what you want it to be able to do 24 24 00:01:11,040 --> 00:01:13,163 and how you want to interact with it. 25 25 00:01:14,020 --> 00:01:18,380 So before we code it, I'm going to just cut this, 26 26 00:01:18,380 --> 00:01:21,230 so keep it saved in your clipboard, 27 27 00:01:21,230 --> 00:01:26,203 and I'm gonna think about how we want to use the item model. 28 28 00:01:27,380 --> 00:01:31,050 Ideally, I would like to be able to create an item, 29 29 00:01:31,050 --> 00:01:34,470 give it the things that an item needs, 30 30 00:01:34,470 --> 00:01:37,860 and get it to load the price 31 31 00:01:37,860 --> 00:01:40,260 or give me the price of the item. 32 32 00:01:40,260 --> 00:01:43,400 So basically, I would like to be able to do something like 33 33 00:01:43,400 --> 00:01:47,880 item is a new item, give it whatever the item needs, 34 34 00:01:47,880 --> 00:01:51,920 which, in my case, is going to be a URL, a tag_name, 35 35 00:01:51,920 --> 00:01:53,920 and a query. 36 36 00:01:53,920 --> 00:01:56,720 And then I would like to be able to item.load_price. 37 37 00:01:58,460 --> 00:02:00,720 Okay, this is 38 38 00:02:00,720 --> 00:02:04,370 essentially the interface of the item, 39 39 00:02:04,370 --> 00:02:07,603 what the item interactions look like. 40 40 00:02:09,470 --> 00:02:12,640 So in order to do this, we do have to, 41 41 00:02:12,640 --> 00:02:14,300 of course, go ahead and create the item 42 42 00:02:14,300 --> 00:02:16,450 and the item is going to have two methods, 43 43 00:02:16,450 --> 00:02:19,220 a constructor method so that we can pass it 44 44 00:02:19,220 --> 00:02:21,710 the URL, the tag_name, and the query, 45 45 00:02:21,710 --> 00:02:24,040 and it's going to have a load_price method 46 46 00:02:24,040 --> 00:02:26,020 that is going to go our web store 47 47 00:02:26,020 --> 00:02:28,250 and it's going to load the price. 48 48 00:02:28,250 --> 00:02:30,270 Essentially, what we're doing is we're taking the code 49 49 00:02:30,270 --> 00:02:34,060 that we had here in app.py at the start of this video 50 50 00:02:34,060 --> 00:02:38,170 and we're going to put it into an item model, an item class, 51 51 00:02:38,170 --> 00:02:42,270 and sort of split it out so it looks a bit better. 52 52 00:02:42,270 --> 00:02:45,950 We're gonna do class Item here in item.py 53 53 00:02:45,950 --> 00:02:48,480 and then we're gonna have an init method, 54 54 00:02:48,480 --> 00:02:50,480 which is gonna do nothing for now. 55 55 00:02:50,480 --> 00:02:53,270 And that's what pass means in Python. 56 56 00:02:53,270 --> 00:02:55,080 It means do nothing. 57 57 00:02:55,080 --> 00:02:57,713 And then we're gonna have a load_price method. 58 58 00:02:59,130 --> 00:03:01,780 And again, pass because we haven't yet decided 59 59 00:03:01,780 --> 00:03:03,320 how we're gonna split this out. 60 60 00:03:03,320 --> 00:03:06,920 Now, in here, I'm gonna paste what I had in my app.py 61 61 00:03:06,920 --> 00:03:08,620 just so we don't lose it 62 62 00:03:08,620 --> 00:03:13,620 and we're going to move this code over into these methods. 63 63 00:03:14,320 --> 00:03:16,560 Now, when you create an item, 64 64 00:03:16,560 --> 00:03:18,850 what we want to do is we want to store 65 65 00:03:18,850 --> 00:03:22,830 all the relevant properties inside the object 66 66 00:03:22,830 --> 00:03:25,320 so that this method can then access 67 67 00:03:25,320 --> 00:03:27,930 those properties that are stored inside itself, 68 68 00:03:27,930 --> 00:03:29,690 the object itself. 69 69 00:03:29,690 --> 00:03:33,070 So those are gonna be the URL, 70 70 00:03:33,070 --> 00:03:35,573 the tag_name, and the query. 71 71 00:03:36,640 --> 00:03:38,090 So let's do that. 72 72 00:03:38,090 --> 00:03:43,090 Self.url is going to be, in this case, this one here. 73 73 00:03:43,150 --> 00:03:45,200 And we're going to improve on this a little bit 74 74 00:03:45,200 --> 00:03:47,210 as we progress through the video 75 75 00:03:47,210 --> 00:03:51,143 so don't be too worried if something isn't what you expect. 76 76 00:03:52,330 --> 00:03:56,693 And then self.query is going to be this. 77 77 00:03:58,320 --> 00:03:59,153 Cool. 78 78 00:03:59,153 --> 00:04:01,760 So of course, we're gonna have to import these things, 79 79 00:04:01,760 --> 00:04:03,730 but we're gonna do that at the top of the file. 80 80 00:04:03,730 --> 00:04:06,810 We'll have to do that because the load_price method 81 81 00:04:06,810 --> 00:04:08,693 is going to require these things. 82 82 00:04:09,890 --> 00:04:12,520 So what is the load_price method gonna do? 83 83 00:04:12,520 --> 00:04:14,740 Well, it's basically gonna do all of this 84 84 00:04:15,830 --> 00:04:19,490 because it's going to go ahead and 85 85 00:04:19,490 --> 00:04:22,440 request this URL, it's going to get the content, 86 86 00:04:22,440 --> 00:04:25,340 then it's going to parse it using Beautiful Soup, 87 87 00:04:25,340 --> 00:04:29,290 and then it's gonna find the element that is related 88 88 00:04:29,290 --> 00:04:32,240 to this item, this tag_name and this query, 89 89 00:04:32,240 --> 00:04:35,263 and then it's gonna sort of get the price and so on. 90 90 00:04:36,583 --> 00:04:38,760 So of course, when we paste that in, 91 91 00:04:38,760 --> 00:04:40,570 we do get a bunch of grey lines 92 92 00:04:40,570 --> 00:04:44,860 and these lines say, Shadows name response from outer scope. 93 93 00:04:44,860 --> 00:04:46,300 So this is not an error. 94 94 00:04:46,300 --> 00:04:48,780 The grey lines are not an error in PyCharm. 95 95 00:04:48,780 --> 00:04:50,220 But what it does say is that 96 96 00:04:50,220 --> 00:04:53,300 you have this variable called response inside this method, 97 97 00:04:53,300 --> 00:04:55,190 but you also have a variable called response 98 98 00:04:55,190 --> 00:04:56,790 outside the method. 99 99 00:04:56,790 --> 00:05:00,510 And so whenever you use the response variables somewhere, 100 100 00:05:00,510 --> 00:05:03,240 so just here, really you're using this one 101 101 00:05:03,240 --> 00:05:05,790 and not the one on the outer scope. 102 102 00:05:05,790 --> 00:05:07,080 And that's fine, that's what we wanna do. 103 103 00:05:07,080 --> 00:05:09,190 But we no longer need this code here 104 104 00:05:09,190 --> 00:05:10,480 because we've already pasted it in. 105 105 00:05:10,480 --> 00:05:11,930 So now, we're gonna delete that 106 106 00:05:11,930 --> 00:05:14,010 and notice that the grey lines go away. 107 107 00:05:14,010 --> 00:05:16,010 Now, we do have some red lines. 108 108 00:05:16,010 --> 00:05:18,610 The red lines are because the URL, tag_name, 109 109 00:05:18,610 --> 00:05:20,710 and query variables that we have earlier 110 110 00:05:20,710 --> 00:05:22,520 are no longer defined. 111 111 00:05:22,520 --> 00:05:24,730 Now that we're inside the method, 112 112 00:05:24,730 --> 00:05:28,720 we do have to use the item properties. 113 113 00:05:28,720 --> 00:05:31,440 So instead of the big, all-caps URL, 114 114 00:05:31,440 --> 00:05:34,470 which was a constant defined outside of the class, 115 115 00:05:34,470 --> 00:05:36,410 we're gonna use self.url, 116 116 00:05:36,410 --> 00:05:40,620 which is going to be the property stored inside self, 117 117 00:05:40,620 --> 00:05:43,220 inside the object that we're currently dealing with. 118 118 00:05:44,150 --> 00:05:46,660 And similarly here, we're gonna use self.tag_name 119 119 00:05:46,660 --> 00:05:48,063 and self.query. 120 120 00:05:49,040 --> 00:05:53,130 Now, at the end, we are gonna say that self.price 121 121 00:05:53,130 --> 00:05:55,720 is the float, without commas. 122 122 00:05:55,720 --> 00:05:58,170 And we're also going to return self.price 123 123 00:05:58,170 --> 00:06:00,930 just in case that the caller of this method 124 124 00:06:00,930 --> 00:06:05,670 wants to use the price immediately without using self.price. 125 125 00:06:05,670 --> 00:06:07,670 Now, we do get another grey line here, 126 126 00:06:07,670 --> 00:06:09,390 another thing that is not an error, 127 127 00:06:09,390 --> 00:06:12,150 but PyCharm is going to make a recommendation. 128 128 00:06:12,150 --> 00:06:15,790 Now, what it says is that you've an instance attribute price 129 129 00:06:15,790 --> 00:06:18,160 defined outside the init method. 130 130 00:06:18,160 --> 00:06:19,710 So this is very important 131 131 00:06:19,710 --> 00:06:22,960 because it's quite an un-Pythonic way of doing things. 132 132 00:06:22,960 --> 00:06:24,740 What it's telling you is 133 133 00:06:24,740 --> 00:06:27,490 inside the init method, you defined three properties, 134 134 00:06:27,490 --> 00:06:31,380 URL, tag_name, and query, and not price. 135 135 00:06:31,380 --> 00:06:34,680 Price is not defined anywhere in here. 136 136 00:06:34,680 --> 00:06:37,750 But you do define self.price 137 137 00:06:37,750 --> 00:06:40,120 in line 23, inside this other method, 138 138 00:06:40,120 --> 00:06:42,420 which is not the init method. 139 139 00:06:42,420 --> 00:06:44,610 You should not do that generally in Python 140 140 00:06:44,610 --> 00:06:46,360 for a simple reason. 141 141 00:06:46,360 --> 00:06:49,640 While it is completely valid code, 142 142 00:06:49,640 --> 00:06:53,590 what you end up with is the information is dispersed 143 143 00:06:53,590 --> 00:06:55,220 between the two methods. 144 144 00:06:55,220 --> 00:06:59,490 The init method tells a reader, whoever is reading this code 145 145 00:06:59,490 --> 00:07:01,560 that there are three properties. 146 146 00:07:01,560 --> 00:07:03,800 But it turns out there is a fourth property, 147 147 00:07:03,800 --> 00:07:06,633 which is hidden away down here in this other method. 148 148 00:07:07,530 --> 00:07:10,850 Ideally, we would want to define all the object properties 149 149 00:07:10,850 --> 00:07:13,030 in the init method so that when you come back 150 150 00:07:13,030 --> 00:07:15,790 and read this code, you can very quickly see 151 151 00:07:15,790 --> 00:07:19,050 what properties are in this object. 152 152 00:07:19,050 --> 00:07:23,010 So we're gonna say self.price equal none. 153 153 00:07:23,010 --> 00:07:25,210 Notice how I'm not using zero 154 154 00:07:25,210 --> 00:07:28,980 because the price of an item after it's been loaded 155 155 00:07:28,980 --> 00:07:30,290 could be zero. 156 156 00:07:30,290 --> 00:07:31,950 I'm using none because that means 157 157 00:07:31,950 --> 00:07:34,820 we haven't loaded the price yet. 158 158 00:07:34,820 --> 00:07:37,090 Once we load the price, this will stop being none 159 159 00:07:37,090 --> 00:07:38,390 and it will be a number. 160 160 00:07:38,390 --> 00:07:41,060 And that number could be zero, unlikely, 161 161 00:07:41,060 --> 00:07:42,583 or it could be something else. 162 162 00:07:44,090 --> 00:07:48,450 Now that we have this here, we can go back into our app.py 163 163 00:07:48,450 --> 00:07:52,610 and we can say that we're gonna import item 164 164 00:07:52,610 --> 00:07:56,010 from models.item import Item. 165 165 00:07:56,010 --> 00:07:57,430 We're gonna import that 166 166 00:07:57,430 --> 00:08:00,693 and we're gonna pass it in the URL, tag_name, and query. 167 167 00:08:01,600 --> 00:08:04,300 But actually, one second, we don't have to do that just now 168 168 00:08:04,300 --> 00:08:06,970 because they are already defined in here. 169 169 00:08:06,970 --> 00:08:10,260 So at the moment, this is what we'll have. 170 170 00:08:10,260 --> 00:08:11,273 We can print it out. 171 171 00:08:14,476 --> 00:08:16,170 And we're gonna press play. 172 172 00:08:16,170 --> 00:08:19,130 And you can see down here we get 1469.0 173 173 00:08:19,130 --> 00:08:21,240 so exactly the same as we had before. 174 174 00:08:21,240 --> 00:08:22,600 And why shouldn't you? 175 175 00:08:22,600 --> 00:08:24,850 You are essentially running the exact same code. 176 176 00:08:24,850 --> 00:08:27,970 We just copied and pasted it and split it up. 177 177 00:08:27,970 --> 00:08:32,940 Now, one of the good things about objects is that 178 178 00:08:32,940 --> 00:08:35,920 you can create objects with different values. 179 179 00:08:35,920 --> 00:08:38,540 So what we're gonna do is we're going to accept 180 180 00:08:38,540 --> 00:08:42,230 the URL, tag_name, and query 181 181 00:08:42,230 --> 00:08:45,300 in the constructor parameters 182 182 00:08:45,300 --> 00:08:49,040 and then we're gonna say self.url is the URL parameter, 183 183 00:08:49,040 --> 00:08:51,780 self.tag_name is the tag_name parameter, 184 184 00:08:51,780 --> 00:08:54,463 and self.query is the query parameter. 185 185 00:08:55,310 --> 00:08:58,190 Good thing about this, you can now go here 186 186 00:08:58,190 --> 00:09:00,270 and notice, by the way, how you get a small error here 187 187 00:09:00,270 --> 00:09:02,980 saying that the parameters are unfilled. 188 188 00:09:02,980 --> 00:09:05,210 So now, we can come back in here and say 189 189 00:09:05,210 --> 00:09:08,570 that the URL is that, the tag_name is that, 190 190 00:09:08,570 --> 00:09:09,670 and the query is that, 191 191 00:09:09,670 --> 00:09:13,430 and we can pass them into this particular item constructor 192 192 00:09:13,430 --> 00:09:14,490 as we have before. 193 193 00:09:14,490 --> 00:09:17,820 I jumped ahead of myself there earlier on the video. 194 194 00:09:17,820 --> 00:09:20,370 But there we go, now we have exactly the same thing. 195 195 00:09:20,370 --> 00:09:21,590 Same thing is running. 196 196 00:09:21,590 --> 00:09:26,410 Only now, we are passing the item URL, tag_name, and query 197 197 00:09:26,410 --> 00:09:28,670 to this particular constructor, 198 198 00:09:28,670 --> 00:09:31,320 which means this item variable 199 199 00:09:32,360 --> 00:09:34,910 is related to this URL. 200 200 00:09:34,910 --> 00:09:38,960 But you could create another item, 201 201 00:09:38,960 --> 00:09:39,880 which has 202 202 00:09:40,860 --> 00:09:45,020 a different URL, but the same tag_name and query 203 203 00:09:45,020 --> 00:09:46,840 if they are from the same website. 204 204 00:09:46,840 --> 00:09:48,610 Of course, if they are from a different website, 205 205 00:09:48,610 --> 00:09:49,740 you're gonna need to find 206 206 00:09:49,740 --> 00:09:51,643 the tag_name and the query separately. 207 207 00:09:52,770 --> 00:09:55,240 Right now, I don't have a second URL 208 208 00:09:55,240 --> 00:09:58,470 with an item that is a valid URL, but you could do this 209 209 00:09:58,470 --> 00:10:01,073 and then this would load the second item. 210 210 00:10:02,000 --> 00:10:04,620 The benefit of that, of course, is that now, your item class 211 211 00:10:04,620 --> 00:10:06,220 is a bit more generic. 212 212 00:10:06,220 --> 00:10:10,480 What you have is the ability to load different items 213 213 00:10:10,480 --> 00:10:12,860 using the same code, whereas before, 214 214 00:10:12,860 --> 00:10:14,610 we didn't really have that ability. 215 215 00:10:16,480 --> 00:10:18,840 All right, so I hope this is helpful. 216 216 00:10:18,840 --> 00:10:22,100 We've now created our item model, which is going to be 217 217 00:10:22,100 --> 00:10:25,100 one of the building blocks of our application. 218 218 00:10:25,100 --> 00:10:28,160 And moving forwards, we're going to be saving these items, 219 219 00:10:28,160 --> 00:10:29,830 we're gonna be able to use them 220 220 00:10:29,830 --> 00:10:32,290 and extract them from a database and so forth, 221 221 00:10:32,290 --> 00:10:34,733 so that we can start building up our app. 222 222 00:10:36,000 --> 00:10:37,550 I'll see you on the next video.