1 00:00:05,104 --> 00:00:10,795 Alright, so we've seen how to keep our data and code separate, and we'll do that again for this program. 2 00:00:10,795 --> 00:00:15,920 So what we want to do is create a new Python file called meal_planner 3 00:00:24,480 --> 00:00:27,360 Alright, so the first thing we're going to do in this new program is to import the 4 00:00:27,360 --> 00:00:36,640 dictionaries from the last video. I'm going to type from contents import pantry comma recipes. 5 00:00:36,640 --> 00:00:40,240 We've seen an import like that previously, in the simple jukebox program 6 00:00:40,240 --> 00:00:45,120 back in the Lists and Tuples section. By importing the dictionaries from content.py, 7 00:00:45,120 --> 00:00:49,280 they become available in this program. So I'm going to check that by printing the dictionaries. 8 00:00:49,280 --> 00:00:59,362 So let's do that, so print parentheses pantry. Next line, print parentheses recipes. 9 00:00:59,362 --> 00:01:01,496 Run the program. 10 00:01:02,560 --> 00:01:07,543 We confirm that our dictionaries are available in this code and it is working. 11 00:01:07,543 --> 00:01:15,449 And we need to scroll the run pane right, as you can see there - the output - to see everything. 12 00:01:15,449 --> 00:01:18,338 Alright, so so far so good. 13 00:01:18,338 --> 00:01:24,160 Next we need to present the recipes to the user so that they can choose one. 14 00:01:24,160 --> 00:01:30,000 I can hear the groans already - not another menu. Once again, we're not learning how to write a menu - 15 00:01:30,000 --> 00:01:34,960 we're learning how to transform data. We display it in a menu, because that lets us see 16 00:01:34,960 --> 00:01:40,480 what we've done to it. Just printing it out would serve the same purpose, but it's more interesting 17 00:01:40,480 --> 00:01:45,040 if there's a use for the transformed data. So how do we transform the data? 18 00:01:46,880 --> 00:01:51,200 So transforming our recipe dictionary, the dictionary values have been replaced with an 19 00:01:51,200 --> 00:01:56,000 ellipsis on the right hand side, just so everything fits on the slide. But you can see that the right 20 00:01:56,000 --> 00:02:03,200 hand side represents our recipes dictionary. We need to transform that to what we can see on the 21 00:02:03,200 --> 00:02:08,720 left hand side. In python that's easy, in fact we can do it with one line of code. Because that would 22 00:02:08,720 --> 00:02:12,720 use something that we'll be covering later, we're going to use three lines of code instead. 23 00:02:13,520 --> 00:02:16,640 Alright, so back to our code. I'm going to paste in the one line that I mentioned. 24 00:02:16,640 --> 00:02:20,400 I'm going to delete the two lines that print out dictionaries. We've confirmed they're available, 25 00:02:20,400 --> 00:02:25,440 and that was the only reason that I printed them. I'm going to paste in this code. 26 00:02:25,440 --> 00:02:29,440 Now don't try to make sense of that line of code. It's called a dictionary 27 00:02:29,440 --> 00:02:34,340 comprehension, and we'll be learning about comprehensions later in the course. 28 00:02:35,200 --> 00:02:39,760 We have to learn to walk before we can run. Obviously you can't learn about dictionary 29 00:02:39,760 --> 00:02:44,800 comprehensions before you've learned about dictionaries, but that leaves me with a quandary. 30 00:02:44,800 --> 00:02:49,120 I have to show you code that makes sense with what we've covered so far, but I'm also 31 00:02:49,120 --> 00:02:54,480 aware that there's a more efficient and pythonic way to write it. To help solve that quandary, I've 32 00:02:54,480 --> 00:02:58,720 presented the more efficient code as a comment. When you come to review these lectures, and the 33 00:02:58,720 --> 00:03:03,840 code samples, that comment will remind you that you should use a comprehension here. 34 00:03:05,200 --> 00:03:09,840 And it will make perfect sense once you've watched the section with comprehensions. Until 35 00:03:09,840 --> 00:03:13,516 then think, of these comments as a reminder to your future self. 36 00:03:13,516 --> 00:03:14,912 Alright, so moving on. 37 00:03:14,912 --> 00:03:20,195 Let's see the more naive way of transforming our recipes into something we can display to the user. 38 00:03:20,195 --> 00:03:24,455 We're going to iterate over the dictionary, and use the keys to create a new one. 39 00:03:24,455 --> 00:03:27,762 Because we're using that new dictionary to display the menu to the user, 40 00:03:27,762 --> 00:03:31,211 I'm going to call it display_dict, 41 00:03:31,211 --> 00:03:37,203 so display_dict equals, and left and right curly braces for an empty dictionary. 42 00:03:37,203 --> 00:03:46,080 On the next line, for index comma key in enumerate parentheses recipes, 43 00:03:46,080 --> 00:03:51,520 and outside of the parentheses there's a colon. So we're creating an empty dictionary on line four. 44 00:03:51,520 --> 00:03:55,443 Next we're iterating over the keys of the dictionary, on line five. 45 00:03:55,443 --> 00:03:58,343 Now we used the enumerate function, when we were working with lists. 46 00:03:58,343 --> 00:04:03,377 If you checked the documentation for enumerate, you'll have seen that it can be used with any iterable. 47 00:04:03,377 --> 00:04:06,560 And if you didn't check the documentation, why not? :-) 48 00:04:06,560 --> 00:04:11,440 Alright, so we're iterating over the tuples that the enumerate function produces. 49 00:04:11,440 --> 00:04:15,760 Each tuple will contain an index, and the key from the dictionary. So let's check what we're 50 00:04:15,760 --> 00:04:23,549 working with, before we write any more code. So we'll just print parentheses index comma key. 51 00:04:24,560 --> 00:04:29,913 So what I'm going to do is move the run pane. We'll run it first 52 00:04:30,720 --> 00:04:35,690 Alright, so I'm going to move this to right top - the run pane - 53 00:04:35,690 --> 00:04:40,640 so we can see the output a bit better. It also keeps it clear of the subtitles. 54 00:04:40,640 --> 00:04:45,280 So the output looks very close to what we want. The indices start at zero which isn't 55 00:04:45,280 --> 00:04:48,880 ideal, but we'll fix that shortly. And if you're thinking Hang on, dictionaries don't 56 00:04:48,880 --> 00:04:54,480 have index numbers, you're right - they don't. They use the keys to index into a dictionary. 57 00:04:54,480 --> 00:04:58,560 The enumerate function creates the index numbers for us. 58 00:04:58,560 --> 00:05:04,637 It iterates over an iterable, and generates an index number for each item it finds, starting at zero. 59 00:05:04,637 --> 00:05:09,841 It then returns tuples, containing the index and value for each item in the iterable. 60 00:05:09,841 --> 00:05:16,960 So we're unpacking each tuple in turn, on line 5, to get the index numbers for each entry in the dictionary. 61 00:05:16,960 --> 00:05:21,280 If you're still a bit unsure about what we've done here, I'll explain it again with a slide. 62 00:05:21,280 --> 00:05:25,600 First, we're going to display our menu repeatedly in a loop, so I'll store these values in 63 00:05:25,600 --> 00:05:31,040 our display_dict dictionary, instead of printing them. I'm going to delete this print line 64 00:05:31,040 --> 00:05:38,720 and replace that with display_dict, and square bracket str parentheses 65 00:05:38,720 --> 00:05:46,880 index, plus one in those parentheses, closing square bracket then equals key. 66 00:05:46,880 --> 00:05:51,280 So I've added one to each index because we don't want the menu to start at zero. I've also converted 67 00:05:51,280 --> 00:05:57,440 the indexes to strings, on line six. Our users will be entering strings and it's much easier to 68 00:05:57,440 --> 00:06:02,800 convert those integer indexes to strings. If we didn't do that, we'd have to convert the user's 69 00:06:02,800 --> 00:06:07,760 input to integers, and we've seen that causes problems if they type in letters. If you wanted 70 00:06:07,760 --> 00:06:12,800 index keys for some reason, then we've written a get_integer function that you could use. 71 00:06:12,800 --> 00:06:18,178 But for this application, it's actually easier to convert the index numbers to strings. 72 00:06:18,178 --> 00:06:22,480 Okay, so before we see the slides I promised, let's print out this new dictionary, 73 00:06:22,480 --> 00:06:27,920 so that we're sure of what we've created. We're going to do that inside the while loop. 74 00:06:27,920 --> 00:06:33,040 Starting on line 8, I'm going to put while True 75 00:06:33,040 --> 00:06:39,000 and a comment here to display a menu of the recipes we know how to cook. 76 00:06:43,920 --> 00:06:50,080 I'll close down the output. I'm going to print parentheses double quotes 77 00:06:52,240 --> 00:06:56,407 Please choose your recipe, 78 00:06:57,280 --> 00:07:05,920 and we'll just put some dash characters as a heading. The actual code next; for 79 00:07:05,920 --> 00:07:16,637 key comma value in display_dict dot items parentheses colon, and print parentheses 80 00:07:16,637 --> 00:07:28,160 f double quotes and key in curly braces, dash then value in curly braces, and we finish off that line. 81 00:07:28,160 --> 00:07:35,520 On line 15, indented to the same level as the for loop, choice is equal to input 82 00:07:35,520 --> 00:07:41,680 parentheses double quotes, colon and a space in those double quotes. Then on line 17, 83 00:07:41,680 --> 00:07:49,130 if choice is equal to zero, two equal signs there, colon break. 84 00:07:51,200 --> 00:07:54,160 So we've seen code like that before - we're iterating over the items of 85 00:07:54,160 --> 00:07:59,251 a dictionary, to display the keys and values. Our display_dict dictionary 86 00:07:59,251 --> 00:08:03,520 has numeric characters as its keys, and the recipes as its values. 87 00:08:03,520 --> 00:08:10,800 What may not be obvious, is that its values are actually the keys from the recipe's dictionary 88 00:08:10,800 --> 00:08:14,640 So we've transformed the data, so that the keys from recipes 89 00:08:14,640 --> 00:08:20,720 becomes the values in display_dict. The keys in our recipes dictionary, on the left, 90 00:08:20,720 --> 00:08:25,840 have become the values for the display_dict dictionary on the right. 91 00:08:26,800 --> 00:08:31,600 The enumerate function takes each of the keys from the dictionary, generates the next number for each 92 00:08:31,600 --> 00:08:37,760 one, and emits both values as a tuple. Our code then takes the first item in each tuple, which is the 93 00:08:37,760 --> 00:08:43,200 number and converts it to a string. It uses that string as the key in the display_dict 94 00:08:43,200 --> 00:08:49,120 dictionary. It uses the second item in the tuple, the recipe name. as the value for that key. 95 00:08:51,040 --> 00:08:55,920 We end up with a new dictionary, the display_dict dictionary, shown on the right. 96 00:08:55,920 --> 00:08:59,760 All the values on the right are valid keys in the recipes dictionary, on the 97 00:08:59,760 --> 00:09:06,240 left. That means we can use those values to access items in the recipes dictionary. 98 00:09:06,960 --> 00:09:11,360 If the user chooses option 3 for a pizza, we can look up pizza in the recipes 99 00:09:11,360 --> 00:09:19,600 to get the list of ingredients for a pizza. So we'll see that working in the next video.