1 00:00:04,660 --> 00:00:09,540 Alright, so let's talk a bit more about nested indexing. At the end of the last video, 2 00:00:09,540 --> 00:00:14,000 I left you experimenting with indices in our nested data structure. You should be 3 00:00:14,000 --> 00:00:18,350 able to get the details for any album and song, from the list. Now if we want 4 00:00:18,350 --> 00:00:22,400 to print the song Mayhem, which I talked about, we need to start with the fourth 5 00:00:22,400 --> 00:00:27,180 album in the list. That's at index position three. So go down to our code here. 6 00:00:27,180 --> 00:00:31,920 So we need to change line 47, to access the fourth album - so we change the 7 00:00:31,920 --> 00:00:38,200 2 to a 3 there. The index for the songs list stays the same - all the songs 8 00:00:38,200 --> 00:00:42,860 lists for each album, are at index position three - so we don't need to change that at all. 9 00:00:42,860 --> 00:00:45,920 But Mayhem is the third song, or is the 10 00:00:45,920 --> 00:00:51,200 third item rather, in the songs for that album, so we use index position 2 for that. 11 00:00:51,200 --> 00:00:57,960 So on line 53, I'll change the 1 to a 2. The song title itself, is at the same position - 12 00:00:57,960 --> 00:01:01,420 position 1 in the tuple - so the rest of the code stays the same. 13 00:01:01,420 --> 00:01:07,340 Run the program. We confirm we get Mayhem printed out. Alright, so let's 14 00:01:07,340 --> 00:01:11,780 see how we can do that all in one go. So we come down, add some code: 15 00:01:11,780 --> 00:01:21,200 line 57, I'm going to type mayhem is equal to albums, left square bracket and 16 00:01:21,200 --> 00:01:25,460 3 in it, another set of square brackets with 3 in it, and another 17 00:01:25,460 --> 00:01:29,750 set of square brackets with 2 in it, and the final set of square brackets 18 00:01:29,750 --> 00:01:36,480 with 1 in it, and let's print mayhem on the next line. 19 00:01:36,480 --> 00:01:41,120 Now before running the program, compare those index numbers with the value's that we've used 20 00:01:41,120 --> 00:01:49,240 on lines 47, 50, 53 and 55. You can probably work out what will be printed. 21 00:01:49,240 --> 00:01:57,420 If not, my choice of variable name's giving it away. Let's run the program and see. 22 00:01:57,420 --> 00:02:01,420 We get Mayhem printed out again. 23 00:02:01,420 --> 00:02:06,960 So I said I was gonna take this slow, and I've just thrown that horrible-looking line 57 at you. 24 00:02:06,960 --> 00:02:11,980 We've seen what it does - now we'll look at how it's done it. I'll take it step by step, 25 00:02:11,980 --> 00:02:18,240 starting with the first index. Let's go and add some code: print albums 26 00:02:18,240 --> 00:02:22,680 and in square brackets, the number 3, then closing parenthesis. 27 00:02:22,680 --> 00:02:28,040 Now albums 3 is the tuple for the Imelda May album. It's got four items, two strings 28 00:02:28,040 --> 00:02:32,690 an int for the year and a list. Let's run that to confirm, and we can see the 29 00:02:32,690 --> 00:02:38,900 output there, confirming that. So looking at that, you can see the list of songs 30 00:02:38,900 --> 00:02:43,020 is at position three, and we can add that index to get just the songs lists. 31 00:02:43,020 --> 00:02:47,140 So let's have a go at doing that. Alright, so I'll duplicate line 60 again. 32 00:02:47,150 --> 00:02:51,049 I'm gonna go down to the end of the line. I'm gonna add to the end of the line, 33 00:02:51,049 --> 00:02:56,870 a 3 in square brackets. And again, that's for the list of songs. Run the program 34 00:02:56,870 --> 00:03:00,700 and we should get the list of songs, and you can see that is the case down the 35 00:03:00,700 --> 00:03:07,880 bottom there. Alright, back on line 47, we bound the variable album to albums 3, 36 00:03:07,880 --> 00:03:12,800 and then on line 50, we bound songs to the item at index position 3 37 00:03:12,800 --> 00:03:18,640 in the album. So looking at the code, line 61 is producing the same thing 38 00:03:18,640 --> 00:03:23,820 without using intermediate variables. So now if we want to print the Mayhem tuple, 39 00:03:23,820 --> 00:03:28,180 we can add index 2 to the end. So let's duplicate the line again, 40 00:03:28,180 --> 00:03:33,220 and come down to the end and add 2 in square brackets. Run the program again to 41 00:03:33,230 --> 00:03:37,579 confirm what we get. This time, you can see we get the third item from the songs 42 00:03:37,580 --> 00:03:42,440 list, which you can see above there - that line of output - the item at position 2. 43 00:03:42,440 --> 00:03:47,380 And that's a tuple, and then we can index into that to get just the title. 44 00:03:47,389 --> 00:03:51,380 So let's have a go at doing that again, duplicate the line again. So I'll add 1 45 00:03:51,380 --> 00:03:58,160 in square brackets, on that line. We'll run it again, and we should see the title 46 00:03:58,160 --> 00:04:01,910 printing out, as you can see, and it is on the screen there. So each index indexes 47 00:04:01,910 --> 00:04:06,109 into the object produced by the previous one, as those four lines of code 48 00:04:06,109 --> 00:04:11,419 demonstrate. Alright, so the next video isn't a video - it's a document giving you 49 00:04:11,420 --> 00:04:14,820 some more things to practice, to help you get used to indexing into a 50 00:04:14,820 --> 00:04:17,680 nested structure. So have a look at that document, 51 00:04:17,690 --> 00:04:21,220 then I'll see you in the video following that.