WEBVTT 0 00:00.450 --> 00:04.920 Now while our snake game works now with all of the functionality that we set out 1 00:04.920 --> 00:05.753 to create, 2 00:06.000 --> 00:11.000 there's just one thing that bothers me a little bit about this code, and it's how 3 00:11.370 --> 00:12.900 wordy this section is. 4 00:13.350 --> 00:18.350 All that we're trying to do is make sure that we're detecting the distance from 5 00:19.200 --> 00:23.130 all of the segments that we're looping through in snake.segments 6 00:23.340 --> 00:24.810 other than the first one. 7 00:25.350 --> 00:29.400 Surely there's an easier way of doing this rather than writing all of these 8 00:29.400 --> 00:34.080 lines of code. And indeed there is. But in order to use it, 9 00:34.290 --> 00:38.520 we have to learn about a Python concept known as slicing. 10 00:39.540 --> 00:44.540 Let's say that we had a list of piano keys all the way from a to g, and we wanted 11 00:46.050 --> 00:49.680 to get hold of a small section of this list. 12 00:50.130 --> 00:54.270 Let's say we wanted to slice the list so that we only get the c, 13 00:54.270 --> 00:58.620 d, and e keys from this list. How would we do that 14 00:58.620 --> 01:00.390 using Python? Well, 15 01:00.390 --> 01:04.830 one way of doing that is you could write a for loop and you could check, well, 16 01:04.830 --> 01:09.300 is it c, is a d, is it d. If so, then add it to a new list. 17 01:09.510 --> 01:12.690 But that's really convoluted. We have a much, 18 01:12.690 --> 01:16.890 much better way of doing that in Python. And it's known as slicing. 19 01:17.400 --> 01:20.940 This is what the syntax would look like. We would get hold of our lists, 20 01:21.000 --> 01:24.750 piano_keys, and then we would use a set of square brackets, 21 01:25.110 --> 01:28.980 but instead of accessing just one item with a position, 22 01:29.400 --> 01:34.400 we get a set of items by slicing it from position 2 to position 5. 23 01:36.360 --> 01:40.770 This might be a little bit confusing because we know that a is that position 24 01:40.770 --> 01:44.220 0, b is at 1, c is at 2, 25 01:44.640 --> 01:49.640 but the one at position 5 is actually f, so how does this get us c, d, and e? 26 01:52.590 --> 01:54.690 Well, you have to visualize it like this. 27 01:55.170 --> 02:00.170 Imagine that zero position is actually at the beginning of the list before where 28 02:00.870 --> 02:04.440 a starts. And at the end of the list, 29 02:04.470 --> 02:07.350 we're actually at the slicing position of 7. 30 02:08.160 --> 02:09.810 If we think about it this way, 31 02:09.870 --> 02:14.870 then the way that we're slicing this list is going all the way from position 2 32 02:15.990 --> 02:20.790 to position 5 then of course, we would end up with c, d, and e. 33 02:22.020 --> 02:24.240 If you take a look at this code in my Repl.it, 34 02:24.420 --> 02:27.000 I've essentially got the same code that we saw in the slides 35 02:27.360 --> 02:31.890 and we're slicing this list of piano keys from position 2 to 5. 36 02:32.370 --> 02:35.790 When I hit run, you will see that what gets printed is c, 37 02:35.790 --> 02:40.320 d, and e, exactly the slice that we wanted. Now, 38 02:40.350 --> 02:43.890 there's other things that you can do with slicing that's pretty cool. So, 39 02:43.890 --> 02:47.130 for example, if you wanted to slice from position 2, 40 02:47.160 --> 02:48.660 which remember is right here 41 02:48.750 --> 02:52.560 because we're starting at 0, 1, and 2, 42 02:52.890 --> 02:56.430 and you want to slice it all the way to the end of the list, well, 43 02:56.430 --> 03:00.820 you can just emit the second number. You can have two and then a colon. 44 03:01.330 --> 03:04.840 Now, when you slice this you get all of the rest of the list 45 03:05.050 --> 03:07.840 starting from the position that you specified. 46 03:08.500 --> 03:10.900 And this works in the opposite direction as well. 47 03:11.320 --> 03:15.790 Let's say that we want to get hold of everything up to position 5. Well, 48 03:15.790 --> 03:18.850 we could omit the first number, add a colon, 49 03:19.030 --> 03:22.510 and then after the colon specify the end slice position. 50 03:22.900 --> 03:27.700 And now we get all of the items in the list up to that position 5. 51 03:28.900 --> 03:32.830 In addition to just slicing between two numbers, 52 03:33.100 --> 03:37.630 we can actually specify a third number after another colon. 53 03:38.290 --> 03:42.790 And what this number does is it sets the increment. For example, 54 03:42.790 --> 03:46.780 we wanted the slice from a position 2 to position 5, 55 03:47.080 --> 03:50.800 but we want to only get every other item. 56 03:51.190 --> 03:54.580 So then it would give c, it would skip over the second one, 57 03:54.670 --> 03:59.050 and then it would give us e. And if I hit run, this is exactly what you see. 58 04:00.460 --> 04:04.000 So let's say I wanted to get hold of everything in this list 59 04:04.450 --> 04:09.400 but I wanted every second item. Well, then this is what my code would look like, 60 04:09.430 --> 04:13.900 go from the beginning to the end and then skip every second one. 61 04:14.590 --> 04:17.140 And I end up with a, c, e, and g. 62 04:18.430 --> 04:21.250 Now to extend this a little bit further, 63 04:21.640 --> 04:26.640 we can actually use this neat trick to specify a -1 as the increment 64 04:27.430 --> 04:32.430 and what this does is it will actually reverse this list for us going from right 65 04:33.040 --> 04:37.300 to the end to the beginning. So essentially the increments are by one, 66 04:37.540 --> 04:41.710 but it's by -1, so that way we get the list starting from the end 67 04:41.950 --> 04:43.210 all the way back to the beginning. 68 04:43.630 --> 04:47.020 And this is a really neat trick that you'll see a lot of people use when it 69 04:47.020 --> 04:51.310 comes to manipulating lists and tuples. So speaking of tuples, 70 04:51.490 --> 04:55.810 this method of slicing also works for tuples. 71 04:56.320 --> 04:58.540 So let's say we had a piano tuple, 72 04:58.570 --> 05:03.570 which remember is defined by a set of parentheses with items inside separated by 73 05:04.120 --> 05:06.220 commas. Well, 74 05:06.220 --> 05:10.780 we can use the same method of slicing to work with our tuple. 75 05:11.140 --> 05:12.880 So we use our square brackets, 76 05:13.180 --> 05:17.230 let's get hold of the items from section 2 to 5. 77 05:17.530 --> 05:20.920 Then when we hit run, you'll see it gives us mi, fa, so. 78 05:20.920 --> 05:25.330 So coming back to our code, I have a challenge for you. 79 05:25.330 --> 05:30.330 Can you figure out how to use what we've just learned about slicing to 80 05:30.610 --> 05:33.850 change this code so that we get rid of this 81 05:33.850 --> 05:38.850 if statement where we're passing over the snake head so that we are in fact only 82 05:39.430 --> 05:44.430 checking that the snake head has a distance to every segment other than the first 83 05:45.040 --> 05:49.870 segment, less than 10? If you managed successfully to do this, 84 05:49.900 --> 05:51.340 you should be able to get rid of this 85 05:51.340 --> 05:56.340 if statement, change this to a single if statement and somehow figure out a way of 86 05:57.590 --> 06:02.590 making this code work using slicing. Pause the video and give this a go. 87 06:05.680 --> 06:06.130 Alright, 88 06:06.130 --> 06:11.130 so we know that we want to loop through every segment in snake.segments 89 06:11.530 --> 06:14.560 other than the first one. Well, 90 06:15.010 --> 06:20.010 all we need to do is simply slice this list of segments. So we can get hold of 91 06:21.640 --> 06:26.290 everything that starts off from position 1 to the end, 92 06:26.620 --> 06:29.350 by writing 1: nothing. 93 06:29.860 --> 06:34.860 This will give us everything inside the list other than the first item, like 94 06:35.740 --> 06:36.573 so. 95 06:37.150 --> 06:42.150 And then we can use that segment to loop through it and then check every segment 96 06:42.490 --> 06:46.840 in the tail against the distance to the head. And now when you run the code, 97 06:47.080 --> 06:50.440 you can see that it works just as perfectly as before, 98 06:51.400 --> 06:56.400 but we've now vastly simplified our code using the power of Python 99 06:56.860 --> 06:57.693 slicing. 100 06:58.600 --> 07:03.160 Have fun playing with your snake game and be sure to let me know your highest 101 07:03.160 --> 07:05.500 score because I can't seem to get past 10. 102 07:05.890 --> 07:09.280 And you've pretty much seen in this tutorial how bad I am at this game, 103 07:09.580 --> 07:13.450 but I'm sure you can do much better. And on top of that, 104 07:13.480 --> 07:17.200 think about ways that you might want to customize your snake game. 105 07:17.530 --> 07:21.370 Maybe you want to change the food to have a different color or a different 106 07:21.370 --> 07:25.210 shape, maybe your snake is actually going to eat turtles, I don't know. 107 07:25.420 --> 07:27.220 The world is your oyster. 108 07:27.430 --> 07:30.760 Now that you've learned about so many more concepts in Programming 109 07:31.000 --> 07:35.620 including inheritance in OOP as well as slicing lists and tuples. 110 07:36.490 --> 07:40.180 So I hope you've had fun building this game and I'll see you tomorrow.