1 00:00:04,670 --> 00:00:10,070 So let's talk about unpacking tuples. Earlier in this section, when we were 2 00:00:10,070 --> 00:00:14,629 looking at lists, I bound several variables to the same value, using a 3 00:00:14,629 --> 00:00:18,800 single assignment. So let's have a go at doing something similar. So we're going 4 00:00:18,800 --> 00:00:27,380 to create a new Python file - I'm going to call it unpacking. 5 00:00:27,380 --> 00:00:38,340 The code was something like this in that previous section: a = b = c = d = e = f = 12. 6 00:00:38,340 --> 00:00:42,880 Then we'll print the value of c. 7 00:00:42,880 --> 00:00:48,260 All six variables are now bound to the same value - 12 in this case. 8 00:00:48,260 --> 00:00:52,550 If we run the program now, we just want to confirm that c has the value 12, and we 9 00:00:52,550 --> 00:00:57,350 can see that is the case on screen. So that's a useful shortcut, or shorthand, 10 00:00:57,350 --> 00:01:01,460 for typing in the full amount of code. It also makes it easier to make 11 00:01:01,460 --> 00:01:05,319 changes, without the risk that you'd forget to change one of the variables. 12 00:01:05,319 --> 00:01:09,320 Let's say that the value of 12 needs to be changed, for whatever reason. With the 13 00:01:09,320 --> 00:01:12,770 assignment all in one line, as we've got on line one, we only need to make the change 14 00:01:12,770 --> 00:01:18,680 in one place, so we change the value of 12 to 42. If we'd used six separate 15 00:01:18,680 --> 00:01:23,860 assignments, I'd have to make the change in six places. Python also lets us bind 16 00:01:23,860 --> 00:01:28,280 several variables to different values. In fact, we've already done that, when we 17 00:01:28,280 --> 00:01:32,520 looked at the enumerate function, earlier. So let's start, now, with a simple example, 18 00:01:32,520 --> 00:01:36,600 before we go back and look at that enumerate code. So down on line 4, 19 00:01:36,600 --> 00:01:44,180 I'm going to type x comma y equals 1 comma 2. Let's print out the value of x, 20 00:01:44,180 --> 00:01:52,369 and also the value of y. So run the program, and we can see there, that x is bound 21 00:01:52,369 --> 00:01:58,160 to the value 1 and y is bound to the value 2. And you're not restricted to just two values. 22 00:01:58,160 --> 00:02:03,860 We could add z if we wanted to, there, as well. So put a comma z there, 23 00:02:03,860 --> 00:02:10,860 and also add the value 76. Let's do that and print out z. 24 00:02:11,800 --> 00:02:20,330 Run - we also get 76 printed out. So this is called unpacking a tuple and is very 25 00:02:20,330 --> 00:02:25,220 useful in all sorts of situations. Looking at that code on line four, 26 00:02:25,220 --> 00:02:29,520 those three values on the right hand side, look suspiciously like a tuple. 27 00:02:29,520 --> 00:02:37,600 That's because they are a tuple. Let's write that code differently. So I'm going to 28 00:02:37,610 --> 00:02:45,680 type on line 9, print parentheses double quotes, unpacking a tuple. Line 11, I'm 29 00:02:45,680 --> 00:02:52,580 going to type data equals 1 comma 2 comma 76 - just a comment here, that 30 00:02:52,580 --> 00:03:02,120 data represents a tuple. Then on the next time we're gonna type x, y, z 31 00:03:02,120 --> 00:03:06,140 is equal to data. Then we can print out the values of x, y and z and I'll 32 00:03:06,140 --> 00:03:10,130 just take a copy of those three lines, that we used previously, and paste them 33 00:03:10,130 --> 00:03:16,310 down here. Run the program, and we should see we get the same output. And you can 34 00:03:16,310 --> 00:03:21,740 see that is the case. On line 12, the three variables, x y and z, get each of the 35 00:03:21,740 --> 00:03:26,700 values from the data tuple. Data on the right hand side, is bound to a tuple. 36 00:03:26,700 --> 00:03:32,520 We did that on line 11. The three variables on the left hand side also look like a tuple, 37 00:03:32,520 --> 00:03:36,920 but they're not. They're three separate variables, that each get a value 38 00:03:36,920 --> 00:03:41,460 from the data tuple. You can't have a tuple on the left of an assignment, 39 00:03:41,460 --> 00:03:45,460 because tuples, if you recall, are immutable. Alright, so we'll finish this 40 00:03:45,470 --> 00:03:49,370 lecture with the second advantage of using a tuple. When I used the phrase, 41 00:03:49,370 --> 00:03:53,630 unpacking a tuple, a few moments ago, I didn't mention that you can unpack any 42 00:03:53,630 --> 00:04:02,000 sequence type. Let's see an example of that. On line 17, I'm going to type print 43 00:04:02,000 --> 00:04:11,540 parentheses double quotes, Unpacking a list. And the code itself, we're going to type 44 00:04:11,540 --> 00:04:18,600 data_list is equal to, in square brackets, it's going to be 12, 13, 14 45 00:04:18,600 --> 00:04:24,220 in the square brackets, and on the next line, I'm going to type p, q, r 46 00:04:24,220 --> 00:04:32,420 equals data_ list. Let's print put the values of p, q and r. 47 00:04:32,420 --> 00:04:37,680 on lines 21 to 23. So data_list, on line 19, 48 00:04:37,680 --> 00:04:42,020 is a list. It contains three items and we can unpack them into three variables, 49 00:04:42,020 --> 00:04:46,820 as we're doing here; p, q and r. That's on line 20. Run the program and let's 50 00:04:46,820 --> 00:04:51,580 confirm that that works. You can see that's working fine, so we can unpack 51 00:04:51,580 --> 00:04:56,600 the values from any sequence type. But lists are mutable, so if something 52 00:04:56,600 --> 00:05:01,250 changes the list, our code will break. You might create a list in one part of your 53 00:05:01,250 --> 00:05:05,690 code, then attempt to unpack it in another part. If you append another item 54 00:05:05,690 --> 00:05:10,010 to the list before then, the code will crash. We can demonstrate that quite 55 00:05:10,010 --> 00:05:18,710 easily. Let's add some code. We'll add it down here, on line 20. So I'm gonna type 56 00:05:18,710 --> 00:05:25,380 data_list.append, and in parentheses, 15, 57 00:05:25,380 --> 00:05:31,600 and put a space there for readability purposes. Now if we run this, 58 00:05:31,600 --> 00:05:36,139 it's crashed, as you can see. So the error happened on line 22, and it actually says, 59 00:05:36,139 --> 00:05:41,330 too many values to unpack, expected 3. Line 22 is where we tried to 60 00:05:41,330 --> 00:05:46,550 unpack the list into three variables, but the list now contains four items and our 61 00:05:46,550 --> 00:05:51,840 code crashed, as a result. If we'd used a tuple instead of a list, that couldn't happen, 62 00:05:51,840 --> 00:05:57,000 and the reason for that is tuples are immutable and you can't append items to a tuple. 63 00:06:15,440 --> 00:06:19,080 These examples have been very simple, and don't really show just how useful 64 00:06:19,080 --> 00:06:23,200 unpacking a tuple might be. I'll stop the video here and in the next video, 65 00:06:23,200 --> 00:06:27,380 we'll see some more practical applications for unpacking tuples. 66 00:06:27,380 --> 00:06:30,400 See you in the next video.