1 00:00:05,360 --> 00:00:09,120 At the end of the last video, I mentioned that our program doesn't tell us how much 2 00:00:09,120 --> 00:00:14,800 of each ingredient we need. The problem is the recipes dictionary. Let's have a look at that, 3 00:00:14,800 --> 00:00:21,520 in contents.py. So each recipe contains a list of ingredients. However, as you can see, 4 00:00:21,520 --> 00:00:27,760 there's no quantities. Adding the quantities is easy - it's just a bit of typing. Deciding how to 5 00:00:27,760 --> 00:00:34,080 add them is harder. So how are we going to store the recipe items, if we want to include the quantities. 6 00:00:34,080 --> 00:00:40,080 There are two obvious options; we could store them as tuples; or as key value pairs - a dictionary, 7 00:00:40,080 --> 00:00:45,200 in other words. I'll open up a Python file that I've created and added to our project, 8 00:00:45,200 --> 00:00:51,360 with two different dictionaries. You can see it's recipe_options.py. Now you can download the 9 00:00:51,360 --> 00:00:56,720 file from the resources for this video. Download recipe_options.txt then copy and paste 10 00:00:56,720 --> 00:01:01,680 into a new Python file, as I've already done. And I've called mine recipe_options.py, as 11 00:01:01,680 --> 00:01:07,520 you can see there. Now to keep things simple, I've only included one recipe in each dictionary; 12 00:01:07,520 --> 00:01:12,720 chicken and chips, and you can see those on screen. The first one, recipes_tuple, the lines 13 00:01:12,720 --> 00:01:19,280 one through eight, uses a list of tuples. The value for the key chicken and chips is a list. 14 00:01:19,280 --> 00:01:25,920 Inside the list we've got four tuples. Each tuple, lines three to six, contains an ingredient name 15 00:01:25,920 --> 00:01:31,680 and the quantity of that ingredient. Below that, we've got our recipes_dict on lines 10 16 00:01:31,680 --> 00:01:37,360 to 17. The value for the key chicken and chips is a dictionary. Within that dictionary, we've got 17 00:01:37,360 --> 00:01:44,960 key value pairs. The value for the key chicken, is 100. This recipe needs 100 grams of chicken. 18 00:01:44,960 --> 00:01:50,000 Now don't worry too much about the units, by the way. In America, you'd probably be referring to 19 00:01:50,000 --> 00:01:56,800 ounces and cups. Many other places will use grams and millilitres. In the UK, they use whatever they 20 00:01:56,800 --> 00:02:02,640 feel like. They buy beer in pints, petrol in litres, and measure fuel consumption in miles 21 00:02:02,640 --> 00:02:07,440 per gallon. We should really be storing the units somehow, so that our program can convert them 22 00:02:07,440 --> 00:02:14,480 into whatever the cook is used to, but I don't want to make things too complicated at this stage. 23 00:02:14,480 --> 00:02:20,320 So how to choose? Okay, so how do we decide which of these data structures will be more appropriate 24 00:02:20,320 --> 00:02:24,720 for our program. This can have new programmers staring at the screen for hours, 25 00:02:24,720 --> 00:02:30,240 unable to proceed. They know they should use one of them, but can't decide which. 26 00:02:30,240 --> 00:02:34,800 If you find yourself in that position, just pick one. Toss a coin, if you like. It's much 27 00:02:34,800 --> 00:02:40,560 better to start doing something, than to sit there in a state of paralysed indecision. 28 00:02:40,560 --> 00:02:46,880 Trust me - if it matters, and you choose the wrong one, you'll soon find out. 29 00:02:46,880 --> 00:02:51,120 Now please note that I'm not suggesting you design your programs by tossing a coin. 30 00:02:51,120 --> 00:02:56,240 Think carefully about the requirements, and what you'll need to do with your data structures 31 00:02:56,240 --> 00:03:00,720 but if you can't decide between different alternatives, then picking one and getting 32 00:03:00,720 --> 00:03:07,840 on with it is much better than doing nothing. If you do nothing, that's what you'll learn - nothing! 33 00:03:07,840 --> 00:03:12,400 If you make a mistake and make the wrong choice, you'll have learnt that it is the wrong choice. 34 00:03:12,400 --> 00:03:17,360 And hopefully, you'll also have learnt why. Here though, it doesn't really matter. 35 00:03:17,360 --> 00:03:23,120 I'll go back to our code, and we'll see what getting the item and quantity looks like, in each case. 36 00:03:23,120 --> 00:03:27,200 Alright, so let's scroll down and look at the code that I've added at the bottom of this recipe 37 00:03:27,200 --> 00:03:32,480 underscore options.py file. Now it might take you a moment to spot the difference. If I hadn't 38 00:03:32,480 --> 00:03:41,040 included the comments on lines 22 and on lines 30, spotting it would be even harder. On line 22, 39 00:03:41,040 --> 00:03:45,120 we unpacked the tuple that we retrieved from the list. You can see each ingredient 40 00:03:45,120 --> 00:03:52,400 and quantity that we unpack, in the output, when we run the program, which I'll do now. 41 00:03:52,400 --> 00:03:58,800 Now on line 30, we iterate over the dictionary's items. That returns the key value pairs as 42 00:03:58,800 --> 00:04:07,200 tuples, and we unpack them in the same way. In both cases, the output is the same, which we'll run again. 43 00:04:07,200 --> 00:04:12,629 So hopefully, that'll give you an idea of why it was difficult to choose between these two approaches - 44 00:04:12,629 --> 00:04:17,440 either one will work fine. We don't need to make changes to the recipe while the 45 00:04:17,440 --> 00:04:22,640 code is running, so we can use either of these data structures. That's not always the case, though. 46 00:04:22,640 --> 00:04:30,320 Let's go back to contents.py. Let's have a look at the pantry dictionary, on lines 1 through 21. When we 47 00:04:30,320 --> 00:04:34,960 tell the program that we're going to make a recipe, the program will subtract the amount of each 48 00:04:34,960 --> 00:04:41,280 ingredient used. We are going to be updating the values in pantry. Using tuples here wouldn't work, 49 00:04:41,280 --> 00:04:47,040 because tuples are immutable. But for our recipes, when including the quantities, we can use either. 50 00:04:47,040 --> 00:04:52,320 Now this is a section on dictionaries, so the obvious one for me to choose is a dictionary. 51 00:04:52,320 --> 00:04:57,200 Now you don't want to type all the quantities into our recipes dictionary, so download the file contents 52 00:04:57,200 --> 00:05:02,720 contents_quantities.txt from the resources for this video. So copy all the text, and paste 53 00:05:02,720 --> 00:05:09,840 it into contents.py, replacing all the code that's already in there. So I'm going to do that right now. 54 00:05:12,400 --> 00:05:14,800 Alright, with that done, we're now ready to get our program to check 55 00:05:14,800 --> 00:05:19,680 the quantity of each ingredient. We'll do that in the next video.