1 00:00:00,030 --> 00:00:01,140 In the last lesson, 2 00:00:01,170 --> 00:00:06,170 we figured out how we can get our turtle race up and running and get our turtles 3 00:00:06,930 --> 00:00:09,270 at the starting positions. Now, 4 00:00:09,300 --> 00:00:13,980 the next job we have is to figure out how we can get these turtles to start 5 00:00:14,010 --> 00:00:18,150 moving. The movement is going to have to be randomized 6 00:00:18,540 --> 00:00:23,540 and each step they take will have to be a random number. That way they don't go 7 00:00:23,580 --> 00:00:24,690 straight to the end 8 00:00:24,960 --> 00:00:28,620 and we end up with a terrible gaming experience. 9 00:00:29,190 --> 00:00:33,360 So what we're going to do is we're going to create a random number, 10 00:00:33,390 --> 00:00:36,000 let's say between 0 and 10, 11 00:00:36,450 --> 00:00:40,860 and then we're going to tell the turtle to go forward by that random amount. 12 00:00:40,860 --> 00:00:43,230 So it could be anywhere between 0 and 10. 13 00:00:43,950 --> 00:00:47,490 And then we're going to get this to repeat itself many, many times. 14 00:00:48,840 --> 00:00:49,740 As you might've guessed, 15 00:00:49,770 --> 00:00:52,740 this is probably going to involve some sort of while loop. 16 00:00:53,160 --> 00:00:58,160 So let's say we start out with a variable called is_race_on and it starts out as 17 00:00:59,460 --> 00:01:00,293 false. 18 00:01:00,570 --> 00:01:05,570 But then once the user has made their bet and we can check to see 19 00:01:05,880 --> 00:01:10,170 user_bet exists, then in that case 20 00:01:10,230 --> 00:01:13,800 we're going to switch that is_race_on to true. 21 00:01:16,050 --> 00:01:20,430 And then we can use our is_race_on inside our while loop. 22 00:01:20,910 --> 00:01:25,910 Now this way we prevent our while loop from starting up while the user is still 23 00:01:25,980 --> 00:01:28,920 deciding on which turtle they're going to bet on. 24 00:01:29,160 --> 00:01:31,020 So it doesn't start prematurely. 25 00:01:31,710 --> 00:01:36,480 Now when the user has made their bet and the race is now on, well 26 00:01:36,480 --> 00:01:40,080 now we're going to need to get hold of a random number. 27 00:01:43,130 --> 00:01:48,130 We're going to use the random module to get hold of a random int between the 28 00:01:49,430 --> 00:01:52,220 range of 0 and 10. 29 00:01:52,610 --> 00:01:55,250 Now randint is actually inclusive, 30 00:01:55,250 --> 00:01:59,060 so the random number could be zero all the way up to 10. 31 00:01:59,780 --> 00:02:03,740 So now we're gonna call this the rand_distance, 32 00:02:04,520 --> 00:02:09,520 and this is going to be the distance that one of our turtles is going to move 33 00:02:09,949 --> 00:02:10,580 forwards by. 34 00:02:10,580 --> 00:02:15,580 So we want some sort of turtle.forward and the distance that it goes forward 35 00:02:18,350 --> 00:02:20,030 is the random distance. 36 00:02:20,750 --> 00:02:23,720 Now we have lots of turtles that we've created, 37 00:02:24,050 --> 00:02:26,240 but we kind of haven't really done anything with them. 38 00:02:26,690 --> 00:02:31,280 What we want to do instead is to have some sort of list of turtle. 39 00:02:31,310 --> 00:02:33,380 So we'll call all_turtles, 40 00:02:34,070 --> 00:02:36,350 and this list starts out as empty. 41 00:02:36,740 --> 00:02:39,290 But every single time we create a new turtle, 42 00:02:39,560 --> 00:02:43,970 then we can append that turtle to this list. So at this stage, 43 00:02:44,000 --> 00:02:47,870 it doesn't really make sense to call all the turtles tim anymore, right? 44 00:02:47,870 --> 00:02:50,900 Because they're all going to be individual instances. 45 00:02:51,470 --> 00:02:56,470 So let's go ahead and refactor and rename this to a new_turtle. 46 00:02:58,900 --> 00:03:03,900 And now what's happening in our for loop is we're creating a new turtle and 47 00:03:04,060 --> 00:03:09,060 each of those new turtles are going to be appended to our all_turtles list. 48 00:03:11,320 --> 00:03:15,730 So now we're going to have a list of multiple turtle instances, 49 00:03:16,270 --> 00:03:20,260 and each of those instances is going to have a different state. 50 00:03:20,530 --> 00:03:21,490 So for example, 51 00:03:21,520 --> 00:03:25,780 they already start out with a different Y-position and a different color. 52 00:03:26,320 --> 00:03:27,340 But later on, 53 00:03:27,400 --> 00:03:31,600 we're also going to get them to move forwards by a different amount. 54 00:03:32,170 --> 00:03:35,560 So we can loop through our list of turtles, 55 00:03:35,590 --> 00:03:38,080 so for turtle in all_turtles, 56 00:03:40,980 --> 00:03:45,980 let's go ahead and create a random distance for each of them and then move that 57 00:03:46,740 --> 00:03:49,320 turtle forward by the random distance. 58 00:03:49,860 --> 00:03:52,050 So now if we run our code 59 00:03:53,670 --> 00:03:55,200 and see it in action, 60 00:03:55,620 --> 00:03:59,580 you can see that once all of the turtles have gone into their starting 61 00:03:59,580 --> 00:04:04,560 positions, they stop creeping along each time by a different amount. 62 00:04:08,190 --> 00:04:12,990 Now, however, our turtles are actually going to keep going until forever. 63 00:04:13,110 --> 00:04:16,140 It's basically a loop that's never going to stop. 64 00:04:16,620 --> 00:04:20,700 So let's think about what the stopping conditions should be. Well, 65 00:04:20,730 --> 00:04:25,730 once any of these turtles have actually reached the end of the screen 66 00:04:26,730 --> 00:04:31,170 which is the X-value of +250, 67 00:04:31,170 --> 00:04:35,820 once they've reached this line, then that's kind of the end of the race, 68 00:04:35,850 --> 00:04:36,683 right? 69 00:04:36,990 --> 00:04:41,490 But a turtle object is a 40 by 40 object. 70 00:04:41,910 --> 00:04:45,390 So if we're only detecting for the 250, 71 00:04:45,660 --> 00:04:48,390 then our turtle would have already overshot. 72 00:04:48,480 --> 00:04:53,480 So instead, we want to detect when the turtle has reached the 230 mark. Back in our 73 00:04:55,230 --> 00:04:56,700 code in our for-loop, 74 00:04:57,060 --> 00:05:01,620 we can check to see if the turtle that we're currently looping through, 75 00:05:02,190 --> 00:05:07,190 if it's X-coordinate is greater than 76 00:05:09,210 --> 00:05:13,710 230. Well, in this case, it's basically won. 77 00:05:14,190 --> 00:05:15,510 Now at this stage, 78 00:05:15,600 --> 00:05:19,890 if we print this current turtle's color, 79 00:05:20,340 --> 00:05:23,370 then you'll actually see something a little bit strange. 80 00:05:25,530 --> 00:05:27,360 You can see that firstly, 81 00:05:27,360 --> 00:05:31,890 it prints multiple values because the while loop is still continuing and the 82 00:05:31,890 --> 00:05:34,020 other turtles continue to go forward. 83 00:05:34,470 --> 00:05:37,770 But the first value is going to be the turtle that won. 84 00:05:38,340 --> 00:05:41,370 And you can see it prints yellow and yellow. 85 00:05:41,880 --> 00:05:45,840 So what's going on here? Well, if we look at this color method, 86 00:05:45,930 --> 00:05:50,790 you can see that you can either use it to set the pen color and fill color, 87 00:05:51,090 --> 00:05:54,720 or it will return the pen color and fill color. 88 00:05:55,170 --> 00:05:56,940 So when it prints out two colors, 89 00:05:57,650 --> 00:06:01,430 the first one is going to be the pen color and the second is going to be the 90 00:06:01,430 --> 00:06:05,720 fill color. So if we only want to know the pen color, 91 00:06:06,050 --> 00:06:10,910 then we can just get hold of the turtle.pencolor. 92 00:06:10,970 --> 00:06:15,290 This is going to be the color of the body of the turtle. So in our code, 93 00:06:15,320 --> 00:06:20,320 we can say that the winning color is equal to the current turtle.pencolor. 94 00:06:25,100 --> 00:06:30,100 And then we can now check to see if the winning color is equal to the user's 95 00:06:31,100 --> 00:06:35,420 bet, because if this is the case, well then the user has won, right? 96 00:06:35,450 --> 00:06:38,090 So we can tell them you've won. 97 00:06:38,330 --> 00:06:41,300 And then we can tell them the color of the winning turtle. 98 00:06:44,200 --> 00:06:45,070 Now, however, 99 00:06:45,070 --> 00:06:49,480 if this is false or rather in the else statement, 100 00:06:49,870 --> 00:06:53,140 well, in that case, we're going to have to print the same thing 101 00:06:53,470 --> 00:06:56,770 but now we're going to tell them that they've lost. 102 00:06:59,020 --> 00:06:59,410 Yeah. 103 00:06:59,410 --> 00:07:03,790 Finally, when the first turtle reaches the X-coordinate, 104 00:07:03,790 --> 00:07:06,160 when this first color gets printed, 105 00:07:06,280 --> 00:07:09,160 we want to stop the while loop. This way 106 00:07:09,160 --> 00:07:12,490 the remaining turtles don't continue to nudge forward 107 00:07:12,790 --> 00:07:17,170 and we get end up with lots of winners like this. So inside this 108 00:07:17,200 --> 00:07:21,520 if statement, when the turtle's X-coordinate has surpassed 230, 109 00:07:21,820 --> 00:07:25,390 we're going to change the is_race_on to false. 110 00:07:26,020 --> 00:07:30,190 Now we're ready to test out our code. And again, 111 00:07:30,190 --> 00:07:34,390 I'm going to bet on the red turtle and I'm going to speed up the playback speed 112 00:07:34,420 --> 00:07:36,640 of this race when I'm editing this video. 113 00:07:37,240 --> 00:07:42,240 And now the game has ended and you can see that the blue turtle is the one that 114 00:07:42,760 --> 00:07:44,920 first got its head across the finish line. 115 00:07:45,460 --> 00:07:50,260 And it tells me just as much. I've lost and the blue turtle is the winner. 116 00:07:51,070 --> 00:07:56,070 So we've now used Python turtle to build a very simple turtle racing game. 117 00:07:56,680 --> 00:08:01,680 And we're starting to use these X and Y positions in the turtle coordinate 118 00:08:02,350 --> 00:08:06,520 system. Now, these coordinates take a little bit of getting used to, 119 00:08:06,850 --> 00:08:11,850 especially thinking about things such as if a turtle is 40 pixels wide, 120 00:08:12,160 --> 00:08:14,770 then in order to get the turtle to the starting line 121 00:08:14,980 --> 00:08:19,300 we have to subtract half of the width of the turtle, which is 20. 122 00:08:19,540 --> 00:08:23,350 So then 250 minus 20 becomes 230. 123 00:08:23,680 --> 00:08:26,740 And it's things like this that takes a little bit of getting used to. 124 00:08:27,220 --> 00:08:31,480 So what I really recommend is to have a play around with these values, 125 00:08:31,750 --> 00:08:36,429 make it smaller, or make it larger, change the size of the screen. 126 00:08:36,730 --> 00:08:41,049 And just until you're really familiar with how the coordinate system works 127 00:08:41,080 --> 00:08:44,620 before you proceed to the next lesson, because as you keep going, 128 00:08:44,620 --> 00:08:48,160 I'm going to presume that you've already had a play around with it and you know 129 00:08:48,160 --> 00:08:50,560 exactly how it works. Now, 130 00:08:50,590 --> 00:08:55,150 the other thing that we saw a lot of in this project is this concept of having 131 00:08:55,380 --> 00:08:59,700 multiple objects created from the same class. So in this case, 132 00:08:59,700 --> 00:09:04,590 we're using the turtle class to construct a turtle object called Timmy, 133 00:09:04,860 --> 00:09:09,860 but we've also got a separate object called Tommy. And Timmy and Tommy are both 134 00:09:10,020 --> 00:09:14,900 Tuttle objects, but they're different instances. So they can act independently, 135 00:09:14,900 --> 00:09:18,110 they can have different appearances, they can have different colors, 136 00:09:18,110 --> 00:09:21,380 different attributes, and also a different speed of movement. 137 00:09:21,830 --> 00:09:26,830 So we've seen in our turtle race that each of these instances can act of their 138 00:09:27,140 --> 00:09:29,690 own accord and have different state. 139 00:09:29,930 --> 00:09:33,860 And that's shown in the different speed of movement and this capability of 140 00:09:33,860 --> 00:09:37,580 creating multiple objects which can act and behave independently 141 00:09:37,880 --> 00:09:42,590 is really the secret to why Object Oriented Programming can be so 142 00:09:42,590 --> 00:09:43,423 powerful. 143 00:09:43,550 --> 00:09:48,050 We can create so many of these objects and get them to do our bidding in various 144 00:09:48,050 --> 00:09:50,480 parts of our program. And in the coming lessons 145 00:09:50,510 --> 00:09:52,970 as we build more and more complex projects, 146 00:09:53,270 --> 00:09:58,130 you'll see this concept of having multiple instances with different state being 147 00:09:58,130 --> 00:10:02,060 shown again and again. And we're going to come to see and enjoy the benefits.