1 00:00:04,700 --> 00:00:09,110 Let's have a look at some examples, to understand how tuples work. So I'm 2 00:00:09,110 --> 00:00:13,140 going to go back to tuples_intro.py from the last video, 3 00:00:13,140 --> 00:00:19,430 and we're going to delete the old code. Alright, so I pasted the code in there to 4 00:00:19,430 --> 00:00:22,970 save some time. Pause the video, then come back when you've caught up with the 5 00:00:22,970 --> 00:00:29,689 typing. Alright, so run the program, which I'll do now. We should see the 6 00:00:29,689 --> 00:00:33,380 Metallica tuple printed out, and you can see that on the screen down there. 7 00:00:33,380 --> 00:00:38,280 So it's a tuple containing three items; We've got an album, Ride the Lightning, 8 00:00:38,280 --> 00:00:44,680 the artist, Metallica, and the year that it was released, 1984. Tuples are a 9 00:00:44,680 --> 00:00:50,440 sequence type, which means we could use indexing, to access the individual items in 10 00:00:50,440 --> 00:00:57,400 the tuple. Let's have a go doing that. So below line 7, I'm going to type print 11 00:00:57,640 --> 00:01:05,180 metallica, then in square brackets, 0. I'm going to do the same for the next two lines. 12 00:01:05,180 --> 00:01:14,440 I'm going to change the index number to one and two; 1, 2, like so. 13 00:01:14,440 --> 00:01:19,759 So the item in index position zero is the album name, and let's actually run this, so we 14 00:01:19,759 --> 00:01:23,659 can actually see all of them. So again, the item at index position zero is the 15 00:01:23,660 --> 00:01:27,920 album name. We can see that printed on the second line of the output. 16 00:01:27,920 --> 00:01:32,480 Next we have the artist on the third line then the year on the last line of the output. 17 00:01:32,480 --> 00:01:35,860 Indexing a tuple works the same as indexing a string or a list. 18 00:01:35,860 --> 00:01:40,760 You provide the index position in square brackets. Now that's caused some 19 00:01:40,760 --> 00:01:45,950 confusion in the past. Even though tuples are created using parentheses, you still 20 00:01:45,950 --> 00:01:50,390 use square brackets to index them, and you can see that, if I close down the run 21 00:01:50,390 --> 00:01:55,729 window now, on lines 8 through 10. When you're indexing something, use square 22 00:01:55,729 --> 00:02:01,840 brackets. That's the same whether the thing you're indexing is a list, a string or a tuple. 23 00:02:01,840 --> 00:02:07,219 Unlike a list, a tuple is immutable. If you attempt to change an item in a 24 00:02:07,219 --> 00:02:11,600 tuple, you'll get an error. So let's actually check that. On line 12 25 00:02:11,600 --> 00:02:19,690 I'm going to type metallica square brackets 0, is equal to Master of Puppets. 26 00:02:20,980 --> 00:02:25,940 Now before I run the program, notice that my IDE's highlighted that line. 27 00:02:25,940 --> 00:02:30,709 If we hover over it, you'll see a message that says here, something similar along 28 00:02:30,709 --> 00:02:35,860 the lines of Tuples don't support item assignment. Now not all IDE's will do this, 29 00:02:35,860 --> 00:02:42,040 but most modern ones will. Now when we run the program, you can see that we've got 30 00:02:42,049 --> 00:02:47,300 an error there; Tuple object does not support item assignment. 31 00:03:29,860 --> 00:03:34,980 Python provides ways to create sequences of a different type. You may have checked out the 32 00:03:34,990 --> 00:03:39,400 list and tuple functions, at the built-in functions table in the documentation, so 33 00:03:39,400 --> 00:03:42,100 let's have a look at that. 34 00:03:43,320 --> 00:03:49,160 So we can see the two functions list and tuple there. I'll just move this up the screen a little bit so we can see it. 35 00:03:49,160 --> 00:03:51,180 Now the documentation may be confusing 36 00:03:51,180 --> 00:03:55,760 because these aren't really functions. They're really Python's equivalent 37 00:03:55,760 --> 00:04:00,220 of a class constructor. Don't worry about that because it will make sense in the 38 00:04:00,220 --> 00:04:04,240 Object-Oriented Programming section of this course. For now, though, you can 39 00:04:04,240 --> 00:04:08,220 pretend that they are functions. The documentation has included them 40 00:04:08,220 --> 00:04:13,640 in a table of built-in functions, so that's not unreasonable to pretend that they are. 41 00:04:13,640 --> 00:04:18,480 So the list function returns a list, using the values in the iterable that's passed 42 00:04:18,488 --> 00:04:23,800 to it. So let's go back to our code, and what I'm going to do is delete that line 43 00:04:23,800 --> 00:04:29,720 that gave us the error. Instead what we're going to do, is type metallica2 44 00:04:29,720 --> 00:04:39,880 is equal to list metallica. We're going to print metallica2. 45 00:04:39,880 --> 00:04:45,000 The list function returns a list using the values in the iterable that's passed to it. 46 00:04:45,000 --> 00:04:50,980 As I mentioned, if we run the program, you can see that we've now got a list 47 00:04:50,980 --> 00:04:55,930 containing the same items as our tuple. The last line of the output is the 48 00:04:55,930 --> 00:05:01,320 same as the first, except it uses square brackets, which indicates a list. 49 00:05:01,320 --> 00:05:05,300 Because we've got a list, we can now change the title of the album. 50 00:05:05,300 --> 00:05:16,200 So let's have a go at doing that. So metallica2 then left square bracket 0 equals, 51 00:05:16,200 --> 00:05:27,240 in double quotes, Master of Puppets. Then we'll print Metallica 2 again. 52 00:05:27,240 --> 00:05:31,860 So we'll run this, and there shouldn't really be any surprises there. 53 00:05:31,860 --> 00:05:36,260 We've covered changing values in lists earlier. So looking at the last line 54 00:05:36,260 --> 00:05:41,260 of the output, we've got an album called Master of Puppets by Metallica, 55 00:05:41,260 --> 00:05:46,260 released in 1984. So when might a tuple be more appropriate? 56 00:05:46,260 --> 00:05:48,960 At this point, I'd like to thank one of the students on this course, 57 00:05:48,960 --> 00:05:52,500 Toni Peralta, for pointing out that the data 58 00:05:52,500 --> 00:05:59,300 is now incorrect. The Master of Puppets album was released in 1986, not 1984. 59 00:05:59,300 --> 00:06:03,420 The original video did mention that tuples help protect the integrity of your data, 60 00:06:03,420 --> 00:06:08,280 but didn't link back to this example, so thanks for that Toni. 61 00:07:00,780 --> 00:07:05,130 You'll see some other examples of tuples being used, when we read data from a 62 00:07:05,130 --> 00:07:11,260 database in section 13. It's important that the data in memory, matches the data 63 00:07:11,260 --> 00:07:16,860 in the database, and using an immutable tuple can guard against unintended changes. 64 00:07:16,860 --> 00:07:22,540 We'll look at another reason, for favoring a tuple, in the next video.