1 00:00:05,200 --> 00:00:08,320 Ok, how did you get on? Working with nested data 2 00:00:08,320 --> 00:00:12,851 structures can be tricky at first, which is why we've given you a lot of practice with them. 3 00:00:12,851 --> 00:00:17,280 They're very common when programming. When you're working with nested data structures, 4 00:00:17,280 --> 00:00:21,360 it's worth experimenting a bit, before trying to write the real code. 5 00:00:21,360 --> 00:00:25,298 For example, you could start by getting the data for a single country. 6 00:00:25,360 --> 00:00:29,428 That will let you see what you're working with. I'll start by doing that: 7 00:01:03,760 --> 00:01:09,170 I made sure our dictionary keys were in lowercase, when adding the keys to the countries dictionary. 8 00:01:09,170 --> 00:01:13,280 You can see that on line 20. To make sure that the user's input matches, 9 00:01:13,280 --> 00:01:19,022 we convert their input to lowercase, by calling the casefold method, on line 24. 10 00:01:19,022 --> 00:01:23,040 We have no control over what the user might type, so I've checked that their chosen country does 11 00:01:23,040 --> 00:01:27,920 exist in our dictionary, on line 25. Line 26 retrieves the value for the 12 00:01:27,920 --> 00:01:32,560 chosen country, then we print it out. Let's see what we're working with. 13 00:01:32,560 --> 00:01:37,224 I'll comment out lines 19 and 22, because the output's getting a bit cluttered, 14 00:01:38,560 --> 00:01:40,374 then run the program. 15 00:01:41,760 --> 00:01:45,577 The program's waiting for input. I'll enter Australia. 16 00:01:47,280 --> 00:01:52,675 The value that we get from the dictionary, on line 26, is another dictionary. 17 00:01:53,760 --> 00:01:56,880 If you're unsure about what you're working with, print it out. 18 00:01:56,880 --> 00:02:00,979 You don't have to write all the code in one go. Write part of your code, 19 00:02:00,979 --> 00:02:05,200 then test it and make sure it's doing what you expect, before you write the next bit. 20 00:02:05,200 --> 00:02:09,520 The program isn't doing what we want yet, but it has shown us what we're working with. 21 00:02:09,520 --> 00:02:13,711 Now that we know what we get from the countries dictionary, the next step is easy. 22 00:02:13,840 --> 00:02:18,000 We can get the capital of the country, by using the key "capital". 23 00:02:19,440 --> 00:02:23,417 Back in IntelliJ, retrieve the value for the key "capital": 24 00:02:31,360 --> 00:02:36,284 Ok, we can add some bells and whistles to this code, but in terms of solving the challenge, 25 00:02:36,284 --> 00:02:39,927 this code should work. I'll run the program to check. 26 00:02:41,600 --> 00:02:43,960 I'll start with Australia again ... 27 00:02:45,280 --> 00:02:50,362 and we get Canberra. That's correct, Canberra is the capital of Australia. 28 00:02:51,440 --> 00:02:57,000 You may have wrapped lines 24 to 27 in a loop, to allow the user to keep entering countries. 29 00:02:57,200 --> 00:03:01,008 That's going to make it easier to test different countries, so I'll do that: 30 00:03:04,160 --> 00:03:06,640 We can also make the output a bit more user-friendly, 31 00:03:06,640 --> 00:03:09,467 and provide some way to break out of the loop: 32 00:03:41,330 --> 00:03:43,867 Alright, run the program again. 33 00:03:45,120 --> 00:03:48,203 This time, I'll enter Bermuda. 34 00:03:49,440 --> 00:03:54,119 The capital of Bermuda is Hamilton. Test the program with a few more countries, 35 00:03:54,119 --> 00:03:58,316 and also enter invalid country names. The program shouldn't crash, 36 00:03:58,316 --> 00:04:02,240 but you may want to print a message if the user enters something that isn't in our dictionary. 37 00:04:02,240 --> 00:04:06,320 I won't do that on video, it's a good exercise for you to try on your own. 38 00:04:06,320 --> 00:04:09,920 That's the challenge completed. I'll finish this video by addressing a 39 00:04:09,920 --> 00:04:13,600 question that a few students have asked. When should you convert the user's 40 00:04:13,600 --> 00:04:18,805 input to upper or lower case? Often, you'll want to convert it as soon as you get it – 41 00:04:18,805 --> 00:04:23,520 as I've done here, on line 25. But that's not always ideal. 42 00:04:23,520 --> 00:04:28,160 Have a look at the output from our program. "bermuda" starts with a lowercase "b", 43 00:04:28,160 --> 00:04:32,400 even though I typed it with a capital "B". If you need to use the original value that 44 00:04:32,400 --> 00:04:36,807 was entered, somewhere in your code, then you have to store it unchanged. 45 00:04:36,880 --> 00:04:41,120 Here, it might be more appropriate to convert to lowercase when we access the dictionary, 46 00:04:41,120 --> 00:04:46,240 rather than as soon as we get the input. That's not quite so easy to do, in this case, 47 00:04:46,240 --> 00:04:52,640 because we use the lowercase string in two places. On line 26, we check if the key exists, 48 00:04:52,640 --> 00:04:58,320 and on line 27 we use it to get the value from countries. In this case, one solution is to convert 49 00:04:58,320 --> 00:05:02,450 to lowercase, and store the lowercase key in another variable: 50 00:05:09,886 --> 00:05:14,616 Now we can use this new variable, on lines 27 and 28: 51 00:05:21,040 --> 00:05:24,597 Enter quit to exit the program, then run it again. 52 00:05:30,080 --> 00:05:32,106 I'll enter Bermuda again, 53 00:05:34,320 --> 00:05:39,600 and we get the capital printed out. The output now has the original case of Bermuda. 54 00:05:39,600 --> 00:05:45,280 Ok, that was a brief digression, to address possible problems when you transform data. 55 00:05:45,280 --> 00:05:50,418 If you'll need the original data in your code, then it's your responsibility to make sure you keep it. 56 00:05:50,480 --> 00:05:53,687 The other goal we had, was allow a country code to be entered, 57 00:05:53,687 --> 00:05:58,500 instead of a country name. We'll see how to do that, in the next video.