1 00:00:05,600 --> 00:00:08,800 In this video, we'll examine the problem with our shopping list. 2 00:00:08,800 --> 00:00:13,600 We'll look at why we've got a problem, but more importantly perhaps, how to fix it. 3 00:00:13,600 --> 00:00:18,560 I'll start with an obvious improvement. It's not perfect, but we can make our list less annoying by 4 00:00:18,560 --> 00:00:26,160 sorting it. So on line 42, I'm going to wrap shopping list in parentheses and put sorted, so sorted, 5 00:00:26,160 --> 00:00:35,446 parentheses, shopping list as the argument. So that's a very simple change. We run the program now. 6 00:00:36,080 --> 00:00:40,400 We enter the same options as last time - that was 4 7 00:00:40,400 --> 00:00:47,680 Egg sandwich, 2 Chicken and chips and 5 Beans on toast, 8 00:00:47,680 --> 00:00:50,434 zero to exit. 9 00:00:50,800 --> 00:00:54,000 Both the bread entries now appear together, and our cook is no longer 10 00:00:54,000 --> 00:00:59,866 having to return to the bakers. Okay, so that's a quick fix but we can do better. 11 00:01:00,320 --> 00:01:03,760 Our add_shopping_item function 12 00:01:03,760 --> 00:01:07,360 can check if the list already contains an item, and update the quantity 13 00:01:07,360 --> 00:01:13,855 if it does. So what I'm going to do is go back to here, line 42. I'm going to undo that change, 14 00:01:14,320 --> 00:01:18,870 and back up to our add_shopping_item function on line 4. 15 00:01:20,000 --> 00:01:24,960 We decided to use a list of tuples, and searching through the list is going to be a bit tricky. 16 00:01:24,960 --> 00:01:30,160 We saw how to use the index method of a list, to find an item, but we don't know what item to 17 00:01:30,160 --> 00:01:36,720 search for. Items in the list are in two parts; an ingredient and a quantity. We know the ingredient 18 00:01:36,720 --> 00:01:43,205 part that we want, but we don't know what quantity it'll have, if it's already in the list. 19 00:01:43,840 --> 00:01:48,640 That means we can't search for a specific tuple. We have to iterate over the list, 20 00:01:48,640 --> 00:01:54,080 and compare the first item in each tuple. Choosing a list of tuples instead of a dictionary, wasn't 21 00:01:54,080 --> 00:01:59,120 the best decision here, but we produced a working program, which doesn't do a bad job. 22 00:01:59,120 --> 00:02:02,320 A couple of videos ago, I suggested that you should just pick one, if you 23 00:02:02,320 --> 00:02:07,840 can't decide which option is best. Here I picked the wrong option - a list of tuples 24 00:02:07,840 --> 00:02:12,160 isn't as suitable as a dictionary, in this case. But it's not the end of the world. 25 00:02:12,160 --> 00:02:18,790 Our program isn't as easy to modify as it could be, but we did produce something that works. 26 00:02:19,440 --> 00:02:24,320 In the process, we've learned something. A dictionary is more appropriate here. 27 00:02:24,320 --> 00:02:27,760 Always strive to produce the best code - that goes without saying - 28 00:02:27,760 --> 00:02:33,360 but don't let indecision hold you back. Alright, so time to fix the problem. So looking at line 29 00:02:33,360 --> 00:02:40,617 14, we want a dictionary instead of a list. So let's change that so it's now a dictionary. 30 00:02:40,617 --> 00:02:47,760 And looking down here on line 40, we're getting a warning; Expected type list, 31 00:02:47,760 --> 00:02:53,440 got dict instead. Our function is expecting a list, but we're now passing a dictionary to it, or dict. 32 00:02:53,440 --> 00:02:58,664 We should change the annotations and the Docstring in our function. 33 00:02:58,720 --> 00:03:07,760 We're gonna change this now, to a dict. I'll change it over here now, our Docstring, to indicate 34 00:03:07,760 --> 00:03:13,280 that is now a dictionary. We've now got a warning on line 6; 35 00:03:13,280 --> 00:03:18,480 Unresolved attribute reference append for class dict. Problem is there, is a dictionary 36 00:03:18,480 --> 00:03:22,160 don't have an append method, but that's okay - we're going to change the function code. 37 00:03:22,160 --> 00:03:27,520 This is also a great opportunity to see another dictionary method. I'll do things the long way 38 00:03:27,520 --> 00:03:33,760 first, so that it's clear what the new method will be doing. So let's delete that line, and replace it 39 00:03:33,760 --> 00:03:42,240 with if item in data colon, data square brackets, and item in those square brackets 40 00:03:42,240 --> 00:03:50,720 plus equals amount. And we'll do an else otherwise on the next line; else colon. It'll be data item in 41 00:03:50,720 --> 00:03:57,360 square brackets equals amount. So that's fairly straightforward. If the item is in the dictionary, 42 00:03:57,360 --> 00:04:03,040 we're using augmented assignment to increase its value by amount. Otherwise, using the else, we store 43 00:04:03,040 --> 00:04:08,800 the amount using item as the key. This adds the entry to the dictionary. Because we're now using a 44 00:04:08,800 --> 00:04:14,000 dictionary instead of a list, we have to get the keys and values. We have done that a few times 45 00:04:14,000 --> 00:04:19,230 now - we use the dictionary's items method. So let's do that. So we're going to add down here; 46 00:04:19,230 --> 00:04:27,840 for things in shopping list.items, parentheses. Let's run the program now and see what we've got. 47 00:04:28,800 --> 00:04:37,760 Same options as before; Egg sandwich, Chicken and chips, Beans on toast, zero to exit. 48 00:04:37,760 --> 00:04:44,868 This time now, there's only one entry for bread with a quantity of 120, so that's much better. 49 00:04:45,600 --> 00:04:49,440 More importantly, we didn't have to make a lot of changes to the program. 50 00:04:49,440 --> 00:04:53,840 In fact, the only changes we made to the main program were because of my bad decision. 51 00:04:53,840 --> 00:04:59,280 But how bad a decision was it really? We had to make a few changes to the code to use a dictionary, 52 00:04:59,280 --> 00:05:03,760 instead of a list of tuples. But we haven't had to completely rewrite everything. In fact, the 53 00:05:03,760 --> 00:05:08,400 changes we needed to make were relatively minor. So hopefully, that's convinced you to 54 00:05:08,400 --> 00:05:14,400 just go ahead and start coding, whenever you can't choose between more than one option. 55 00:05:14,400 --> 00:05:19,680 It didn't take long to realize that my decision wasn't the best one, and it was easy to fix. 56 00:05:19,680 --> 00:05:24,400 When you've gained more experience, and are working on much larger programs, then changes will be 57 00:05:24,400 --> 00:05:29,280 more costly. But don't let indecision hold you back, especially while you're learning. 58 00:05:29,280 --> 00:05:32,320 Have a go and make mistakes. You'll learn a lot from your mistakes. 59 00:05:32,320 --> 00:05:36,800 You learn nothing from doing nothing, as I've said previously. Alright, so moving on. 60 00:05:36,800 --> 00:05:42,480 In the next video, we'll look at the alternative code I mentioned. See you in that next video.