1 00:00:04,680 --> 00:00:08,840 Alright, so let's talk about nested data structures in more detail. 2 00:00:08,840 --> 00:00:12,980 We've had a think about how we're going to represent the songs in our list of albums. 3 00:00:12,980 --> 00:00:17,820 Now at the moment, we've defined albums as a list on line 1 of this file - 4 00:00:17,820 --> 00:00:22,640 tuples_intro.py. Inside the list, we've got five tuples. 5 00:00:22,640 --> 00:00:26,220 I'm going to take this slow, because nested data structures is 6 00:00:26,220 --> 00:00:30,179 something that new programmers often find confusing, but they're really quite 7 00:00:30,179 --> 00:00:33,870 straightforward, once you get the hang of them. But at first, they can seem very 8 00:00:33,870 --> 00:00:38,010 complicated. So let's start by adding some songs to each of the tuples in the 9 00:00:38,010 --> 00:00:44,000 list. So we're going to create a new Python file here, called nested_data. 10 00:00:51,200 --> 00:00:56,250 So we recommend that you type in all the code in this course. Typing the code 11 00:00:56,250 --> 00:01:00,720 really helps you get used to the syntax, and if you make errors, then fixing them 12 00:01:00,720 --> 00:01:04,559 is great practice. But typing data's just boring, so what I'm gonna do here is 13 00:01:04,559 --> 00:01:08,700 paste in the data. You can get what I've pasted it, in in the resources section for 14 00:01:08,700 --> 00:01:15,280 this video. So copy the contents to your clipboard and paste them in. 15 00:01:15,280 --> 00:01:19,340 Alright, so that's what I've pasted in. You can see that we've got a list here, 16 00:01:19,350 --> 00:01:25,110 containing four tuples, just as we had before. Each tuple now contains four 17 00:01:25,110 --> 00:01:29,370 items. So we've got the album title, artist and year - you see an example of 18 00:01:29,370 --> 00:01:33,180 that on line two - and that's just like it was before, but now we've also got 19 00:01:33,180 --> 00:01:37,040 a list in each tuple. You can see the first list, starting on line three, 20 00:01:37,040 --> 00:01:42,080 extending down to line nine. Now, we can use a for loop to print out the items in 21 00:01:42,090 --> 00:01:45,420 each tuple, and it's going to be very similar to our previous for loop. 22 00:01:45,420 --> 00:01:49,170 We'll just add an extra variable for the songs. So let's go down to the bottom of the 23 00:01:49,170 --> 00:01:55,409 source code and add that. So I'm going to type for name comma artist comma year 24 00:01:55,409 --> 00:02:01,409 comma songs in albums : I'm just going to print them out, so print 25 00:02:01,409 --> 00:02:07,760 parentheses, and in double quotes Album : left and right curly brace comma, and we're 26 00:02:07,760 --> 00:02:11,360 going to do the same for the other three. So we've got Artist : 27 00:02:11,360 --> 00:02:16,120 left and right curly braces comma Year : left and right curly braces comma 28 00:02:16,120 --> 00:02:21,280 and finally Songs : left and right curly braces closing double quote. 29 00:02:21,280 --> 00:02:25,560 On the next line I'm going to type dot format, and in parentheses name comma 30 00:02:25,560 --> 00:02:33,840 artists comma year comma songs. Let's run the program and then check the 31 00:02:33,840 --> 00:02:37,680 output carefully there. Now the first three items in each album are simple 32 00:02:37,680 --> 00:02:41,730 variables, the title artist and year. The fourth item is a list, and we can see 33 00:02:41,730 --> 00:02:45,390 that there on screen, if I scroll over a little bit, we can see the various 34 00:02:45,390 --> 00:02:50,040 songs there. Now that's at index position 3, and we get the list of songs for any 35 00:02:50,040 --> 00:02:55,920 album by indexing into an album's lists. Now as I said I'm going to take this 36 00:02:55,920 --> 00:03:00,630 slowly. We can do things a lot more concisely than I'm about to do, but it's 37 00:03:00,630 --> 00:03:04,860 easier to understand if I break it down first. So I'm going to start by getting a 38 00:03:04,860 --> 00:03:12,120 reference to the budgie album - that's this third album starting on line 23. So 39 00:03:12,120 --> 00:03:15,720 in the code I'm going to actually type we'll separate the outputs so I'm just going to do 40 00:03:15,720 --> 00:03:23,400 a print in parentheses on line 45, on line 47 I'm going to type album equals albums and square 41 00:03:23,400 --> 00:03:27,120 brackets and two within the square brackets then we'll print album on the 42 00:03:27,120 --> 00:03:35,310 next line. Run this, and we can see the entry there for Budgie's Night Flight 43 00:03:35,310 --> 00:03:41,310 album. Now we can also index into the album tuple, to get the songs. The list 44 00:03:41,310 --> 00:03:50,780 of songs is at index position 3. Then come down here and type songs equals 45 00:03:50,780 --> 00:04:02,270 album 3 in square brackets print songs in parentheses. Now run this 46 00:04:02,270 --> 00:04:08,850 and you can see we've now got just the list of songs there, on screen. Now we're 47 00:04:08,850 --> 00:04:13,620 not done yet. We can get any particular song by indexing into the list of songs. 48 00:04:13,620 --> 00:04:17,820 So let's have a go at doing that. Down here on line 53 I'm going to type song 49 00:04:17,820 --> 00:04:28,370 equals songs and one in square brackets print, in parentheses song. Run this 50 00:04:29,180 --> 00:04:34,199 and we can see that song is a tuple. It's track number two, and the item is 51 00:04:34,199 --> 00:04:39,300 Keeping a Rendezvous. Now if we just want the title, we can index into the tuple 52 00:04:39,300 --> 00:04:45,990 to get the item at position one. Let's have a go at doing that. So I'm going to 53 00:04:45,990 --> 00:04:50,849 type print in parentheses song and one in square bracket, or brackets rather, 54 00:04:50,849 --> 00:04:54,500 and then I'm going to do that and run it. 55 00:04:55,789 --> 00:05:01,469 And you can see we get the song title Keeping a Rendezvous in the output. 56 00:05:01,469 --> 00:05:05,729 There's nothing very complicated about this, it's just indexing. If the item we 57 00:05:05,729 --> 00:05:10,680 get is another list or tuple, we can index into that. If that's also a list or 58 00:05:10,680 --> 00:05:15,090 a tuple then we can index again. Experiment with different albums and 59 00:05:15,090 --> 00:05:18,960 songs, and use the correct index numbers to refer to them in the albums list. 60 00:05:18,960 --> 00:05:25,889 Now as an example, looking at this code again, change the indices so that the 61 00:05:25,889 --> 00:05:30,780 last line of output is Mayhem, from the Imelda May album. In the next video 62 00:05:30,780 --> 00:05:36,650 we'll see how we can do this more concisely. See you in the next video