WEBVTT 0 00:00.330 --> 00:03.570 In the last lesson, we managed to figure out how to get the turtle 1 00:03.780 --> 00:08.340 to move with a keypress and that's with every press of the Up key 2 00:08.610 --> 00:11.040 the turtle moves further towards North. 3 00:11.730 --> 00:15.300 Now the next task is to create and move the cars. 4 00:15.930 --> 00:20.930 The cars need to move from right to left and they need to be randomly generated 5 00:21.060 --> 00:23.460 along the Y-axis here. 6 00:23.970 --> 00:28.970 So they need to be generated right to the right edge of the screen and they can 7 00:29.460 --> 00:31.920 appear anywhere along this line, 8 00:32.220 --> 00:36.840 and then they're going to move automatically towards the left at a fixed pace. 9 00:37.530 --> 00:38.160 Each of these cars, 10 00:38.160 --> 00:43.160 you can see, are going to be turtles and they're going to be 20 by 40 11 00:43.740 --> 00:46.770 pixels. So we mentioned that by default 12 00:46.860 --> 00:50.490 every turtle that we create is 20 by 20 pixels. 13 00:50.940 --> 00:54.480 So we'll need to stretch the turtle to make it into this shape. 14 00:55.500 --> 01:00.150 Now that we are concerned with the cars let's create our code inside the car 15 01:00.150 --> 01:00.983 manager. 16 01:01.680 --> 01:06.680 The first thing we'll need to do is to import the turtle class from the turtle 17 01:06.900 --> 01:11.900 module and our car manager is going to have a init where we create all of our 18 01:14.790 --> 01:18.780 cars. So I'm going to create a list called all_cars, 19 01:19.320 --> 01:23.280 and it's going to start out being an empty list. Now, 20 01:23.310 --> 01:24.420 at some point, 21 01:24.810 --> 01:29.810 our main.py is going to call a function from the car_manager called create_ 22 01:30.570 --> 01:31.403 cars. 23 01:31.740 --> 01:36.740 And this method is going to create a random car somewhere along the Y-axis with 24 01:38.670 --> 01:42.780 a given dimension. Each of these cars, 25 01:42.900 --> 01:47.900 so let's call it a new_car, is going to be a turtle object and it's going to be 26 01:48.630 --> 01:52.680 created in a square shape. Now, in addition, 27 01:52.710 --> 01:56.370 we're going to have to change the dimensions of this turtle 28 01:56.730 --> 01:59.730 and we're going to use that method that we used before 29 02:00.000 --> 02:02.100 which is this one, shapesize. 30 02:02.670 --> 02:05.940 Now, what shapesize allows us to do, if you remember, 31 02:06.030 --> 02:11.030 is it allows us to stretch our turtle along the width and along the length. 32 02:11.700 --> 02:15.150 So we want the width to be double the original size, 33 02:15.180 --> 02:20.180 so two times 20 pixels is 40 pixels and the length we don't want to be stretched 34 02:21.090 --> 02:21.510 at all. 35 02:21.510 --> 02:26.510 So we're going to say it's one times the original length. In addition our new 36 02:27.210 --> 02:31.050 car is not going to draw, so we're going to get it to penup. 37 02:31.710 --> 02:36.710 And also our new car is going to have a random color. So we can set the color and 38 02:38.400 --> 02:43.400 then we can import the random module so that we can use one of these colors in 39 02:44.520 --> 02:45.353 this list. 40 02:45.960 --> 02:50.960 And we can say random.choice and then pass in our list of colors from this 41 02:52.620 --> 02:55.680 COLORS constant. Finally, 42 02:55.710 --> 02:59.980 we're going to define where it's going to go on the screen. To do that 43 03:00.040 --> 03:03.820 we need to define a random_y position. 44 03:04.360 --> 03:08.110 So this again is going to be created from the random module and we're going to 45 03:08.110 --> 03:13.110 use the randint and then we're going to define somewhere along this Y-axis, 46 03:14.050 --> 03:18.220 which is the vertical, somewhere for this call to be generated at. 47 03:18.880 --> 03:22.630 So we know that our screen is 600 by 600, so 48 03:23.110 --> 03:27.730 that means the Y-axis goes from +300 to -300. 49 03:28.090 --> 03:31.900 But we don't want the car to be generated all the way to the edge because 50 03:31.900 --> 03:35.800 remember the turtle needs a bit of starting space and also a bit of ending 51 03:35.800 --> 03:38.830 space. So you can play around with this number, 52 03:38.860 --> 03:43.360 but I've ended up going with -250 to +250. 53 03:44.140 --> 03:49.140 This means that we get a good range in the middle of the screen and that the 54 03:49.300 --> 03:53.830 turtle has a bit of empty space at the beginning and also at the end when it 55 03:53.830 --> 03:58.090 needs to move across. So now that we've defined our random_ 56 03:58.090 --> 04:03.090 y, we can tell our new_car to go to the x position 57 04:03.670 --> 04:07.030 which is going to be the very edge of the right screen, 58 04:07.300 --> 04:10.540 so that's going to be +300, right to the edge. 59 04:10.960 --> 04:15.960 And then the y position is going to be the random_y that we just created. 60 04:17.590 --> 04:20.170 And finally, once we've created our new_car, 61 04:20.380 --> 04:25.380 we're going to append it to our list of all_cars which of course, 62 04:26.650 --> 04:31.090 because it's defined in a class, it has to have the self in front of it. 63 04:32.110 --> 04:35.830 So self.all_cars.append, 64 04:36.160 --> 04:39.730 and then we're going to append this new car that we've just created. 65 04:40.780 --> 04:43.120 Now, coming back to our main.py, 66 04:43.450 --> 04:48.010 let's create our car_manager from the CarManager class, 67 04:48.490 --> 04:51.910 and then we're going to use it inside our game loop here 68 04:52.030 --> 04:55.150 so that on every refresh of the screen, 69 04:55.450 --> 04:57.070 every 0.1 seconds, 70 04:57.370 --> 05:01.330 we're going to get the car_manager to create a new car. 71 05:03.010 --> 05:08.010 And strictly this probably shouldn't be plural because each time we call this 72 05:08.470 --> 05:11.500 method, it only creates one new car. 73 05:11.980 --> 05:15.670 So let's change that method so that it only creates one car, 74 05:15.880 --> 05:18.910 but it creates one car every 0.1 seconds. 75 05:19.930 --> 05:23.260 Now at this point in time if we run our code, 76 05:23.560 --> 05:28.560 you'll actually see nothing happen because the cars are being created at this 77 05:29.500 --> 05:30.640 right edge here 78 05:30.820 --> 05:34.630 and it's not yet visible on the screen. To make it visible 79 05:34.630 --> 05:37.660 we have to move our cars across the screen. 80 05:38.440 --> 05:43.440 Let's create another method which we'll call move_cars because this method is 81 05:43.960 --> 05:46.420 going to go through our list of cars, 82 05:46.690 --> 05:50.230 so for car in self.all_cars, 83 05:50.770 --> 05:55.150 and for each of those cars, it's going to move it towards the left 84 05:55.330 --> 05:58.370 by the move distance that we've defined up here. 85 05:59.270 --> 06:02.240 So to do that, all we need is to get the car 86 06:02.480 --> 06:07.460 to move backwards by the starting move distance. 87 06:08.210 --> 06:12.740 Now it's going to loop through our list of all_cars that were created 88 06:13.190 --> 06:14.750 and then for each of the cars, 89 06:14.780 --> 06:18.260 it's going to move it backwards by five paces. 90 06:18.890 --> 06:23.890 So now in addition to getting the car manager to create a new car on every 91 06:24.470 --> 06:26.030 refresh of the game loop, 92 06:26.360 --> 06:31.160 we're also going to get it to move all of the cars by five paces. 93 06:31.700 --> 06:32.540 Let's hit run 94 06:32.540 --> 06:37.160 now and you should see that we've got our cars being generated, 95 06:37.580 --> 06:42.580 but notice how I've made a slight error in the stretch. Instead of stretching it 96 06:43.160 --> 06:46.670 along the length, I've stretched it along the width 97 06:47.060 --> 06:50.810 and this is why we've got this random array of shapes moving. 98 06:51.320 --> 06:56.320 So let's go back to our car manager and change the width to stretch by one and 99 06:56.870 --> 07:01.160 stretch to the length by two. So now if we rerun our code, 100 07:01.490 --> 07:04.070 you can see the cars are now the right shape, 101 07:04.700 --> 07:08.600 a rectangle that looks like it's moving to the left. 102 07:09.680 --> 07:11.690 Now notice how, in my case, 103 07:11.750 --> 07:15.260 the cars are being generated far too frequently. 104 07:15.260 --> 07:20.210 We've got way too many calls and it's impossible for our turtle to cross the 105 07:20.210 --> 07:21.043 road. 106 07:21.260 --> 07:26.260 So we need to figure out a way of how we can reduce the number of cars that are being 107 07:26.720 --> 07:29.780 made. Instead of creating a car 108 07:29.960 --> 07:34.700 every 0.1 seconds at every refresh of the game, 109 07:35.090 --> 07:37.280 we need to slow this down a little bit. 110 07:37.970 --> 07:42.650 And one way we can do this is by using a random number. 111 07:43.310 --> 07:47.210 Let's say that we create a random_chance 112 07:47.780 --> 07:51.080 which is going to be a one in six chance, 113 07:51.110 --> 07:55.250 so it's almost like throwing a dice. If you get a one on the dice, 114 07:55.580 --> 07:56.780 then we create a car. 115 07:57.290 --> 08:00.740 We can do this by getting hold of our random module, 116 08:00.950 --> 08:04.490 creating a random int between one and six 117 08:05.120 --> 08:10.120 and then we can say that if the random_chance is equal to one, 118 08:12.020 --> 08:15.920 then, and only then do we actually create a new car. 119 08:16.430 --> 08:21.430 So this basically ensures that every six times the while loop runs a new car will 120 08:23.930 --> 08:24.980 be generated. 121 08:25.430 --> 08:29.900 Now it's not going to be precisely every six times because there's some degree 122 08:29.900 --> 08:33.500 of chance involved. But notice when we run our program 123 08:33.500 --> 08:38.500 now, see how the cars are now being created much less frequently. 124 08:39.620 --> 08:43.130 And we've actually got some space for our turtle to cross. 125 08:43.880 --> 08:48.880 So that is how we create and move our cars across the screen and make sure that 126 08:49.580 --> 08:53.450 they don't occur so frequently that our turtle has no chance of crossing the 127 08:53.450 --> 08:57.150 road. I hope this walkthrough was helpful. 128 08:57.360 --> 09:01.320 Don't worry if your code doesn't look the same as mine, it doesn't have to. 129 09:01.770 --> 09:06.270 What matters is if you're able to achieve the desired functionality of the game. 130 09:06.660 --> 09:09.240 There are a million different ways that you can solve this problem. 131 09:09.450 --> 09:13.110 And as long as it works, whatever way you choose will be the best way.