Would you like to inspect the original subtitles? These are the user uploaded subtitles that are being translated: 1 00:00:00,390 --> 00:00:03,150 All right. So now that you've learned about functions, 2 00:00:03,300 --> 00:00:07,680 I have a coding challenge for you. If you head over to this link, 3 00:00:07,800 --> 00:00:12,300 which is in the course resources and head over to this challenge 4 00:00:12,300 --> 00:00:13,710 which is called Hurdle 1, 5 00:00:14,310 --> 00:00:19,310 the idea is that we've got a robot here which needs to do a number of hurdles to 6 00:00:19,590 --> 00:00:23,190 jump over each of these barriers, to get to the final goal here. 7 00:00:23,820 --> 00:00:27,900 Now you need to use your knowledge of functions 8 00:00:28,140 --> 00:00:30,810 as well as some of the things you've learned before, such as the 9 00:00:30,810 --> 00:00:34,920 for loop or the range function, to be able to achieve this. 10 00:00:35,640 --> 00:00:39,810 Now, remember that you can tell the robot to move by typing, move(), 11 00:00:40,290 --> 00:00:43,350 and when that's run, it will move by one space. 12 00:00:43,890 --> 00:00:46,200 And you can also use, say, 13 00:00:46,230 --> 00:00:50,160 turn_left to get the robot to turn left. 14 00:00:50,700 --> 00:00:52,320 And in this case, when I run the code, 15 00:00:52,320 --> 00:00:55,530 it's going to move one space and face to the left. 16 00:00:56,640 --> 00:00:59,130 In order to complete this entire challenge, 17 00:00:59,190 --> 00:01:03,030 you can see there's a number of steps that the robot has to go through before it 18 00:01:03,030 --> 00:01:07,830 can get to this final goal. And if you were to write out each of these steps, 19 00:01:08,160 --> 00:01:12,360 like I have done here one after the other, it would take many, 20 00:01:12,390 --> 00:01:16,950 many tens of lines of code. And that's not what we're about. We're programmers. 21 00:01:16,980 --> 00:01:18,660 So we're born to be lazy. 22 00:01:19,080 --> 00:01:23,400 Try and see if you can minimize number lines of code while still keeping your 23 00:01:23,400 --> 00:01:28,400 code readable and understandable by somebody else and be able to get your robot 24 00:01:28,710 --> 00:01:33,300 to complete these instructions and take the robot to the final goalpost. 25 00:01:34,140 --> 00:01:36,930 And once you've completed the challenge successfully, 26 00:01:37,200 --> 00:01:42,200 you should get a green popup that says you're at the correct X and Y position. 27 00:01:42,990 --> 00:01:44,520 So pause the video now, 28 00:01:44,550 --> 00:01:48,150 head over to this link and give this challenge a go. 29 00:01:48,390 --> 00:01:49,223 Right. 30 00:01:54,290 --> 00:01:57,050 All right. So how did you get on with this challenge? 31 00:01:57,830 --> 00:02:02,720 How many lines of code did it take you to tell this robot to get to the goal? 32 00:02:03,560 --> 00:02:06,230 All right. Let's have a think about how we might tackle this. 33 00:02:06,500 --> 00:02:10,460 We know that out of the things that we can tell the robot to do, the most useful 34 00:02:10,460 --> 00:02:13,190 things are to move and to turn left. 35 00:02:13,670 --> 00:02:17,480 But because the robot doesn't have a builtin turn right function, 36 00:02:17,720 --> 00:02:19,820 then we have to define that ourselves. 37 00:02:20,360 --> 00:02:23,750 And the reason why we need to do that is because you can see that at several 38 00:02:23,750 --> 00:02:27,920 points during the hurdle, we'll have to turn right. For example, 39 00:02:27,920 --> 00:02:32,570 when the robot is here at 2, 2, it will have to turn right, 40 00:02:32,630 --> 00:02:35,810 and then move and then turn right again and then move. 41 00:02:36,290 --> 00:02:39,650 So let's create a new function called turn_right. 42 00:02:40,190 --> 00:02:44,990 So we start out with the def key keyword and then give our function a name which 43 00:02:44,990 --> 00:02:46,280 is going to be turn_right. 44 00:02:47,270 --> 00:02:50,180 And then we add the parentheses with nothing inside 45 00:02:50,210 --> 00:02:52,880 because we're not passing any inputs to this function. 46 00:02:53,360 --> 00:02:58,360 We're just going to use this function as a way of defining turn left three 47 00:02:59,350 --> 00:03:03,970 times. So when you turn left three times, of course you turn right. 48 00:03:04,480 --> 00:03:07,330 And now we have the ability to turn right. 49 00:03:07,870 --> 00:03:12,280 So notice how this is the code block for our turn right function 50 00:03:12,730 --> 00:03:16,690 and it ends at the last line, which is indented, which is line 4. 51 00:03:17,230 --> 00:03:19,030 So every subsequent line 52 00:03:19,060 --> 00:03:22,560 which starts at the very beginning of the code file next to 53 00:03:22,580 --> 00:03:27,430 the left margin is outside this code block and it will act independently. 54 00:03:28,000 --> 00:03:28,810 So in fact, 55 00:03:28,810 --> 00:03:33,430 the first line of code that actually runs in our file is going to be this line 56 00:03:33,430 --> 00:03:36,760 6. And you can see that when I press run, 57 00:03:36,820 --> 00:03:39,370 you can see that's the first thing that gets highlighted. 58 00:03:40,030 --> 00:03:42,340 And if I go through this step wise, 59 00:03:42,400 --> 00:03:47,260 you can see the first line is going to be line 6 and it tells the computer to 60 00:03:47,260 --> 00:03:51,520 go and find this function called turn_right. So if I skipped to the next step, 61 00:03:51,700 --> 00:03:55,930 it's found that, and it's going to start going through lines 2, 3, 62 00:03:55,930 --> 00:03:56,763 and 4, 63 00:03:57,040 --> 00:04:02,040 turning our robot three times until it has turned right. Now that we have the 64 00:04:03,970 --> 00:04:05,440 ability to turn right, 65 00:04:05,560 --> 00:04:10,560 let's have a think about how we might be able to get our robot to make one jump. 66 00:04:11,440 --> 00:04:16,440 Let's see. The first thing we'd probably want our robot to do is to move forwards 67 00:04:16,570 --> 00:04:19,120 by one step, which should take it here. 68 00:04:19,630 --> 00:04:24,630 And then the next thing we want it to do is the turn left so that it faces the 69 00:04:24,760 --> 00:04:25,593 top. 70 00:04:28,680 --> 00:04:28,940 Right? 71 00:04:28,940 --> 00:04:31,220 And once it's in this position, 72 00:04:31,250 --> 00:04:34,580 then we want to get it to move forward one step, 73 00:04:35,210 --> 00:04:39,920 and then we'll probably want it to turn right. Now, 74 00:04:39,950 --> 00:04:44,950 notice how I'm actually testing my code at pretty much every other line that I 75 00:04:45,260 --> 00:04:46,093 write. 76 00:04:46,400 --> 00:04:50,570 And this means that you don't end up in a situation where you get to the end and 77 00:04:50,570 --> 00:04:54,020 you've written lots and lots of lines of code, and it doesn't work. 78 00:04:54,530 --> 00:04:58,430 In which case you have to comb through all of the code you've written and find 79 00:04:58,430 --> 00:05:01,190 out where the problem is. So in this case, 80 00:05:01,220 --> 00:05:04,310 we've only got four lines and we've been testing it step wise. 81 00:05:04,700 --> 00:05:09,020 So we can see that we're on track and our robot is now turned to the right, 82 00:05:09,350 --> 00:05:11,210 ready to move one more step. 83 00:05:13,670 --> 00:05:15,350 And then once it gets to here, 84 00:05:15,350 --> 00:05:18,410 we have to turn right again and move one more step. 85 00:05:23,980 --> 00:05:24,280 Right? 86 00:05:24,280 --> 00:05:27,910 And now it should end up here, but let's just check it out. 87 00:05:28,630 --> 00:05:32,230 So our robot turns left turns right, turns right again. 88 00:05:32,650 --> 00:05:35,110 And it ends up here facing the bottom. 89 00:05:35,710 --> 00:05:40,480 So the final thing we need to do is to get it, to turn left once more, 90 00:05:42,010 --> 00:05:44,350 so that it will face the forward direction. 91 00:05:47,630 --> 00:05:47,900 Right? 92 00:05:47,900 --> 00:05:50,750 So once you've confirmed that your code is working, 93 00:05:51,230 --> 00:05:54,110 then you should really think about what is the next step, 94 00:05:54,140 --> 00:05:57,950 because we've managed to make one hurdle. And notice how, 95 00:05:57,980 --> 00:06:01,700 when we're at this position, 3,1, this particular square, 96 00:06:02,120 --> 00:06:05,000 it's almost the same as if we were at 1, 1, 97 00:06:05,120 --> 00:06:10,040 because we have to move one step again, turn left, move, turn right, move, 98 00:06:10,070 --> 00:06:12,080 turn, right, move, turn left. 99 00:06:12,380 --> 00:06:17,380 So it's basically repeating all of these instructions, rather than executing 100 00:06:18,140 --> 00:06:22,490 these instructions six times, because there are six hurdles. 101 00:06:23,120 --> 00:06:25,430 So if I go back and I start, 102 00:06:25,520 --> 00:06:28,910 then you'll see that this code actually will complete the challenge. 103 00:06:31,980 --> 00:06:32,813 Right? 104 00:06:32,820 --> 00:06:35,790 It says I'm done. And we're at the correct position, 105 00:06:35,940 --> 00:06:38,160 but notice how many lines of code we've got. 106 00:06:38,160 --> 00:06:41,340 We've got something like 58 lines of code. 107 00:06:41,400 --> 00:06:44,700 I know I've left some spaces in their so that you can see which parts are 108 00:06:44,700 --> 00:06:49,290 repeating, but still that's a massive amount of code for something very simple. 109 00:06:49,860 --> 00:06:53,040 Now we know that we can use functions to package 110 00:06:53,100 --> 00:06:55,680 a set of instructions together under one name, 111 00:06:56,040 --> 00:06:58,560 just like what we've done here with the turn_right. 112 00:06:58,920 --> 00:07:02,010 We've packaged the three lines of code turn left, turn left, turn 113 00:07:02,010 --> 00:07:05,040 left into a single function called turn_right 114 00:07:05,460 --> 00:07:09,930 so that when we need that functionality, all we need to do is just the call 115 00:07:09,930 --> 00:07:12,360 the function and add the parentheses at the end. 116 00:07:12,960 --> 00:07:17,550 So we can do exactly the same thing with this set of instructions, 117 00:07:17,610 --> 00:07:21,360 which basically gets our robot to perform a single jump. 118 00:07:22,050 --> 00:07:25,260 So let's create a def and let's call this function jump. 119 00:07:25,920 --> 00:07:30,420 And then lets add the parentheses and the colon. And very importantly, 120 00:07:30,450 --> 00:07:34,590 all of these lines of code must be indented. So to indent 121 00:07:34,590 --> 00:07:36,090 a whole block of code together, 122 00:07:36,330 --> 00:07:41,330 you hold down the command key and click the left square bracket or the right 123 00:07:41,460 --> 00:07:45,600 square bracket. On windows it's holding down the control key and again, 124 00:07:45,600 --> 00:07:48,450 the last square bracket or the right square bracket. 125 00:07:49,140 --> 00:07:54,140 So now this basically says that all of these instructions live inside this block 126 00:07:54,660 --> 00:07:58,890 of code called jump. And when we call jump, 127 00:07:59,760 --> 00:08:03,300 then it will carry out all of these lines of code. 128 00:08:04,680 --> 00:08:09,680 So now what we could do to complete the challenge is to simply call this 129 00:08:09,810 --> 00:08:11,610 function jump six times. 130 00:08:12,690 --> 00:08:13,523 Right? 131 00:08:14,740 --> 00:08:19,740 And so now we could again solve this entire problem using just 21 lines of code. 132 00:08:23,050 --> 00:08:28,050 And we managed to complete this challenge using two functions that have repeated 133 00:08:28,720 --> 00:08:32,560 instructions and then calling the jump function six times. 134 00:08:33,130 --> 00:08:37,750 But because we've learned about loops and the range function, 135 00:08:38,110 --> 00:08:41,350 we know that we can actually cut this down even shorter. 136 00:08:41,890 --> 00:08:44,290 So instead of calling jump six times, 137 00:08:44,320 --> 00:08:49,320 we could actually write a for loop that loops through and calls this jump 138 00:08:50,290 --> 00:08:50,860 function 139 00:08:50,860 --> 00:08:55,860 six times. We could say something like for step in, 140 00:08:56,880 --> 00:09:00,090 and remember that these two key words come from the 141 00:09:00,090 --> 00:09:02,730 for...in loop and they always have to stay the same. 142 00:09:03,480 --> 00:09:05,280 And then after the in keyword, 143 00:09:05,400 --> 00:09:09,600 we define the rules for how many times we want our loop to repeat. 144 00:09:10,050 --> 00:09:13,020 In my case, I'm going to use in range function. 145 00:09:13,530 --> 00:09:17,370 And I'm going to say from 0 to 6, 146 00:09:17,700 --> 00:09:22,380 but not including 6. So in this case it will be 0, 1, 2, 147 00:09:22,410 --> 00:09:23,910 3, 4, 5. 148 00:09:24,270 --> 00:09:27,420 So that actually going to happen six times. 149 00:09:28,020 --> 00:09:32,070 And now I'm going to add the colon. And finally, 150 00:09:32,160 --> 00:09:33,930 inside this for loop, 151 00:09:33,960 --> 00:09:37,650 I'm going to call jump just once. Now, 152 00:09:37,650 --> 00:09:41,790 watch what happens. First it starts off at the for loop, 153 00:09:42,180 --> 00:09:47,180 it calls jump and it goes through this once and then it comes back loops again, 154 00:09:47,880 --> 00:09:51,690 calls it the next time. And then again, 155 00:09:51,840 --> 00:09:55,680 the third time in the loop, fourth time in the loop, 156 00:09:56,280 --> 00:09:59,520 fifth time in the loop and six time in the loop. 157 00:10:01,880 --> 00:10:03,500 How far did you manage to get? 158 00:10:03,950 --> 00:10:08,630 Did you get stuck on this section where we needed to create the for loop? 159 00:10:09,200 --> 00:10:10,610 Well, in that case, 160 00:10:10,640 --> 00:10:14,840 I recommend going back to the lesson where we covered for loops and reviewing 161 00:10:14,840 --> 00:10:19,520 the for loop and the range function in detail before you come back and try to 162 00:10:19,520 --> 00:10:21,980 solve this challenge again. It's really, 163 00:10:21,980 --> 00:10:26,600 really important at this stage that you've understood and you've mastered some 164 00:10:26,600 --> 00:10:31,250 of these ideas because we're going to be using them more and more in the future. 165 00:10:31,910 --> 00:10:35,360 Really make sure that you've understood things before you keep going. 15983