1 00:00:00,180 --> 00:00:04,680 In this lesson we will be programming the drones to go on a patrol flight. 2 00:00:04,700 --> 00:00:07,820 We have been going through each move that the drone can make. 3 00:00:07,830 --> 00:00:13,140 But in this lesson we will have the drone automatically continue as certain patrol routine. 4 00:00:13,140 --> 00:00:19,130 For example you can set your draw to go into the next room and fly back as your patrol route. 5 00:00:19,140 --> 00:00:20,070 Now let's get started. 6 00:00:21,230 --> 00:00:25,410 First we want to import a library called context lib. 7 00:00:25,430 --> 00:00:30,610 Go to the drill manager in it we set sell petrol event. 8 00:00:30,880 --> 00:00:35,250 We will be setting a threading event eventually but we will set it to none. 9 00:00:35,320 --> 00:00:42,310 In the beginning we will be setting a method to start and stop the patrol so we can set the details 10 00:00:42,310 --> 00:00:43,540 there. 11 00:00:43,540 --> 00:00:47,170 Next we set self is patrol to false. 12 00:00:47,170 --> 00:00:51,180 This will be a flag to see if the drone is on a patrol or not. 13 00:00:51,190 --> 00:00:57,750 Then we set a self patrol semaphore and set threading semaphore followed by one. 14 00:00:57,880 --> 00:01:03,870 This threading semaphore will manage to have only one thread while patrolling. 15 00:01:03,880 --> 00:01:10,110 Next we set thread patrol to none we've completed four attributes. 16 00:01:10,110 --> 00:01:16,670 Now we can go on to creating the methods scroll all the way down under the flip methods. 17 00:01:16,710 --> 00:01:21,930 I'll move the codes away so we have a cleaner view for this lesson. 18 00:01:22,080 --> 00:01:27,120 We start defining the patrol method which will start the patrol. 19 00:01:27,120 --> 00:01:34,840 First we need to check if the drone is currently not armed patrol by setting if not self is patrol. 20 00:01:34,840 --> 00:01:39,250 Next we set the patrol event to a threading event. 21 00:01:39,250 --> 00:01:43,170 Next we set thread patrol to threading thread. 22 00:01:43,300 --> 00:01:51,040 The target will be self underscore patrol and args will be set to self patrols and for and self patrol 23 00:01:51,040 --> 00:01:53,260 event as a tuple type. 24 00:01:53,500 --> 00:01:59,850 Set the underscore thread patrols start to start once the patrol starts. 25 00:01:59,900 --> 00:02:03,550 Self is patrol will become true. 26 00:02:03,590 --> 00:02:07,250 Next we define the under school patrol method. 27 00:02:07,250 --> 00:02:09,980 We need to set the argument to Semaphore and stop. 28 00:02:09,980 --> 00:02:13,430 Event. 29 00:02:13,670 --> 00:02:20,900 Next we'll be setting the semaphore is acquire set to Semaphore with the acquire method followed by 30 00:02:20,900 --> 00:02:25,940 blocking equals false by setting blocking equals false. 31 00:02:25,940 --> 00:02:29,220 The second thread will be blocked. 32 00:02:29,450 --> 00:02:32,480 What happens is that the first thread is acquired. 33 00:02:32,480 --> 00:02:38,000 If a second thread is acquired the process will wait to finish the first thread to go onto the second 34 00:02:39,680 --> 00:02:40,540 in this case. 35 00:02:40,550 --> 00:02:46,310 We set the blocking to false which means the process will immediately finish the second thread if it 36 00:02:46,310 --> 00:02:48,100 were to be acquired. 37 00:02:48,110 --> 00:02:48,970 Now let's move on. 38 00:02:49,820 --> 00:02:53,600 If the thread is acquired we can set a logger here. 39 00:02:53,600 --> 00:02:59,960 Action will be sent to patrol and status to acquire. 40 00:02:59,980 --> 00:03:08,740 Here we set a width statement with context lib using as it stack as stack we said stack with callback 41 00:03:08,770 --> 00:03:13,650 which will be invoked once the statement process finishes. 42 00:03:13,660 --> 00:03:18,450 Here we set the semaphore release method to finish the process. 43 00:03:18,580 --> 00:03:21,700 Initially we set the status to zero. 44 00:03:21,700 --> 00:03:25,140 We will count up the number so that the drone knows what to do. 45 00:03:26,510 --> 00:03:32,270 While not stop event is set the status will count up. 46 00:03:32,270 --> 00:03:35,400 If status is 1 the drone will go up. 47 00:03:35,630 --> 00:03:40,460 If status is to the drone will rotate clockwise 90 degrees. 48 00:03:40,460 --> 00:03:45,160 These settings is free for you to decide if status is 3. 49 00:03:45,170 --> 00:03:53,110 The drone will go down if status is for the status will go back to 0 after each move. 50 00:03:53,120 --> 00:03:59,330 We will make the drone hover for five seconds once the stop event is invoked. 51 00:03:59,380 --> 00:04:03,800 The while loop needs to break once the loop is broke. 52 00:04:03,850 --> 00:04:10,720 The stack callback will be invoked using the context lib exit stack. 53 00:04:10,720 --> 00:04:18,560 We are able to create a stack of release methods but here will only set one if you are used to Python 54 00:04:18,560 --> 00:04:18,980 2. 55 00:04:18,980 --> 00:04:23,930 You may be using try except finally with Python 3. 56 00:04:23,930 --> 00:04:28,580 This will be the new code style so remember how to use this context. 57 00:04:28,580 --> 00:04:30,190 Lib exit stack 58 00:04:33,640 --> 00:04:37,900 in case the threat is not acquired the process will finish. 59 00:04:37,900 --> 00:04:43,370 We can also set a logger to see if there were any cases where the thread was an acquired. 60 00:04:43,570 --> 00:04:51,160 We set logger warning with action underscore patrol and status not acquired. 61 00:04:51,160 --> 00:04:58,750 Once we have finished underscore patrol we will go on to set the stop patrol method defined stop patrol 62 00:04:58,750 --> 00:04:59,910 method. 63 00:05:00,040 --> 00:05:03,570 If the drone is in patrol we want to stop it. 64 00:05:03,850 --> 00:05:13,990 Set self patrol event set let's set retried to 0 while thread patrol is alive. 65 00:05:14,020 --> 00:05:17,190 We want to wait four point three seconds. 66 00:05:17,260 --> 00:05:18,580 Then we try again. 67 00:05:18,580 --> 00:05:22,280 Up to 300 if it goes up to 300. 68 00:05:22,300 --> 00:05:27,380 The Loop will break retrial needs to count up. 69 00:05:27,560 --> 00:05:31,010 Lastly we need to set is patrol as follows. 70 00:05:32,180 --> 00:05:38,810 Once the patrol event is set this while loop will be broken then the semaphore will be released and 71 00:05:38,810 --> 00:05:41,670 we'll be able to start a new thread. 72 00:05:41,690 --> 00:05:45,120 Some of you may think that the semaphore is unnecessary. 73 00:05:45,380 --> 00:05:49,310 So I'll explain it to you why we set it here. 74 00:05:49,320 --> 00:05:55,100 This patrol method will be invoked if is patrol is not true. 75 00:05:55,410 --> 00:06:02,610 The thread will run and right after the thread starts the drone will start the patrol in this case there 76 00:06:02,610 --> 00:06:05,820 is a high chance that the second thread will not run. 77 00:06:05,820 --> 00:06:06,920 Based on this code. 78 00:06:07,590 --> 00:06:13,860 But if you were to be using a web application and we invoke the patrol method twice at the same time 79 00:06:14,430 --> 00:06:17,190 then a thread may run twice at the same time. 80 00:06:19,390 --> 00:06:25,700 The chances that this happens may be very low but to avoid it to happen we need to set the semaphore 81 00:06:25,720 --> 00:06:27,280 to be sure. 82 00:06:27,280 --> 00:06:32,920 I hope you understand that this is an advanced way of programming with python and a way to minimize 83 00:06:32,920 --> 00:06:34,660 errors to occur. 84 00:06:34,810 --> 00:06:37,940 You just learned how to set a semaphore and use it. 85 00:06:37,950 --> 00:06:42,430 Context lib that are advanced Python coding while you program your drone. 86 00:06:43,150 --> 00:06:46,610 What a great way to strike two birds with a stone. 87 00:06:46,630 --> 00:06:51,370 Now we are ready to set the commands after the drone takes off. 88 00:06:51,370 --> 00:06:58,780 We will set to go on a patrol using the patrol method we'll set time sleep to 45 seconds before the 89 00:06:58,780 --> 00:07:00,300 patrol stops. 90 00:07:00,520 --> 00:07:04,550 Then the drone will land and complete the process. 91 00:07:04,560 --> 00:07:08,070 Now let's round the code. 92 00:07:08,170 --> 00:07:10,130 You can see the drone take off. 93 00:07:10,420 --> 00:07:13,270 Now it waits for the patrol method. 94 00:07:13,480 --> 00:07:20,890 You'll see that the patrol has started when the word acquire shows as a log first command will go up. 95 00:07:21,070 --> 00:07:27,760 Then make a clockwise turn 90 degrees and goes down after the drone goes down. 96 00:07:27,780 --> 00:07:34,360 The status will go back to zero and the drone will go onto its second patrol routine again. 97 00:07:34,590 --> 00:07:35,520 It flies up 98 00:07:38,900 --> 00:07:40,310 turns 90 degrees 99 00:07:44,000 --> 00:07:51,350 and goes down once you decide on a patrol routine the drone will automatically continue the routine 100 00:07:51,410 --> 00:07:53,140 until the patrol comes to a stop. 101 00:08:02,100 --> 00:08:09,610 Once the stop method invokes the patrol loop will be broken and the drone will land and finish its process. 102 00:08:10,080 --> 00:08:12,450 So that's all for our patrol lesson. 103 00:08:13,500 --> 00:08:14,760 See you in the next lesson.