WEBVTT 00:00.370 --> 00:07.270 In this laboratory lesson, we will create a simple Python action server that calculates the Fibonacci 00:07.270 --> 00:08.050 sequence. 00:08.470 --> 00:16.090 By implementing these actions, we will have a practical example of how to use the Ros two actions and 00:16.090 --> 00:22.330 then we will use this as a template for implementing a more complex application in the upcoming lesson 00:22.360 --> 00:23.230 of the course. 00:24.290 --> 00:29.990 If you are only interested in the C plus plus development, then you can skip to the next lesson in 00:29.990 --> 00:33.860 which we are going to implement the same action server in C plus plus. 00:35.550 --> 00:41.880 In this lesson, we want to use the two actions to implement a node that calculates the Fibonacci sequence. 00:42.360 --> 00:49.690 In mathematics, the Fibonacci sequence, also known as Golden sequence, is a sequence of integers 00:49.710 --> 00:56.010 numbers where each number is the sum of the two preceding ones, except for the first two numbers, 00:56.010 --> 00:58.890 which are by definition zero and one. 00:59.250 --> 01:03.630 The length of the Fibonacci sequence is defined as the order. 01:03.630 --> 01:09.900 For example, the first two numbers of this sequence indicate the order, one of this sequence. 01:09.930 --> 01:16.230 Then the order two of the sequence is represented by the other number one, which is the sum of the 01:16.230 --> 01:17.730 two preceding numbers. 01:17.730 --> 01:22.620 And then the order three of this sequence is represented by the number two and so on. 01:22.650 --> 01:25.170 The sequence continues indefinitely. 01:26.150 --> 01:32.240 Diction server we are going to implement in this lesson will receive the order of the Fibonacci sequence 01:32.240 --> 01:39.620 as a goal and will return the entire Fibonacci sequence up to the requested order as an output referred 01:39.620 --> 01:41.990 to as the result of the action. 01:42.320 --> 01:49.730 So let's add this node that contains the action server in the Arduino bot Pi examples package. 01:49.730 --> 02:01.040 So here in the Arduino Pi example sub folder, let's create a new file called Simple Action Server dot 02:01.040 --> 02:01.310 pi. 02:01.880 --> 02:09.110 As usual, let's start by importing the Pi library and then still from this library. 02:09.110 --> 02:18.290 So from the Pi, from the node modules, let's import the node class and let's use it to define a new 02:18.290 --> 02:18.860 node. 02:19.190 --> 02:25.400 So let's define a new class called Simple Action Server. 02:25.400 --> 02:29.700 And this one inherits from the Node class. 02:29.970 --> 02:33.420 And then let's start by defining the constructor of this class. 02:34.080 --> 02:41.220 So the init function that is a member of this class and within the constructor, the first thing that 02:41.220 --> 02:44.250 we do is to call the constructor of the base class. 02:44.250 --> 02:45.870 So of the node class. 02:46.830 --> 02:54.390 So let's call the init function of the base class to which we pass the name of the node that we call 02:54.390 --> 02:58.140 simple Action server. 02:58.720 --> 03:07.930 Now to create an action server inside this node, let's import from the SQL Pi Library and this time 03:07.930 --> 03:14.200 from the action module, let's import the definition of the Action server class. 03:14.200 --> 03:17.740 And now let's create this class to instantiate a new object. 03:17.740 --> 03:25.210 So here in the constructor, let's create a new variable called Action Server. 03:25.330 --> 03:29.440 As an instance of the Action server class. 03:29.440 --> 03:34.930 And this class is responsible for creating and managing the communication of an action server. 03:35.320 --> 03:39.640 The constructor of this class takes as input the Ross to node. 03:39.640 --> 03:45.220 So the implementation of the node class, which is the current object. 03:45.220 --> 03:47.140 And so the simple action server. 03:47.140 --> 03:53.140 This is our implementation and we access to this one with the self variable. 03:53.140 --> 03:57.520 So we refer to the simple action server with the variable self. 03:57.880 --> 04:03.410 It also takes as input the communication interface that has to be used for the communication with the 04:03.410 --> 04:03.950 action. 04:03.950 --> 04:10.700 And so the interface which specifies how the goal, the feedback and the response messages for the communication 04:10.700 --> 04:12.260 with the action are done. 04:12.710 --> 04:15.470 So let's start by defining this interface. 04:15.470 --> 04:22.430 And once again, as this is a Ros two interface, we can define it within the Arduino Bot messages package. 04:22.640 --> 04:30.710 And so here in this package, as we defined the interface with a service in the SRV folder to define 04:30.710 --> 04:36.380 the interface with an action, we need to create a new folder called Action. 04:36.380 --> 04:43.400 And this folder let's create a new file called Fibonacci Dot Action. 04:43.400 --> 04:49.190 And here we need to indicate how the goal result and feedback messages are done. 04:49.760 --> 04:52.460 So let's start with the goal message. 04:53.750 --> 05:00.110 And this is composed by a single integer that indicates the order of the Fibonacci sequence that we 05:00.110 --> 05:01.850 want the server to calculate. 05:02.150 --> 05:06.740 So this is an integer and is called order. 05:06.920 --> 05:14.420 Next, let's use three dashes and then let's also define the result message. 05:14.630 --> 05:20.810 And so the result message should contain a list of integer, this time representing the full Fibonacci 05:20.840 --> 05:23.360 sequence that was calculated by the server. 05:23.570 --> 05:30.080 So let's use an array of integers and let's call this one sequence. 05:30.080 --> 05:37.400 And finally, still, by using three dashes, let's also define the feedback message. 05:37.400 --> 05:43.730 And so the message that the server will send periodically whenever we add a new element to the sequence. 05:43.730 --> 05:52.010 And also this one is an array, so an array of integers and let's call this one partial sequence. 05:52.220 --> 05:54.380 So let's save this interface. 05:54.380 --> 06:00.950 And now let's make sure that this interface is installed and also it's usable by other node by modifying 06:00.950 --> 06:04.130 once again the file Cmakelists.txt. 06:05.130 --> 06:10.020 Now still in the Ros generate interfaces instruction. 06:10.020 --> 06:13.370 We can also define the interface with an action. 06:13.380 --> 06:22.830 And so let's define the interface that we declared in the action folder and that is called Fibonacci 06:23.490 --> 06:24.900 dot action. 06:25.260 --> 06:27.000 Let's save this file. 06:27.000 --> 06:29.990 And finally in the package dot XML. 06:30.000 --> 06:34.850 So here of the Arduino bot messages, let's also add a dependency. 06:34.860 --> 06:44.580 So here let's add a dependency from the action messages. 06:44.580 --> 06:49.290 And now we can finally save also this file and we can move on. 06:49.290 --> 06:55.980 And so we can build our workspace so that the new interface, the Fibonacci action interface is compiled 06:55.980 --> 06:59.490 and we can start using it within our simple action server. 06:59.910 --> 07:01.620 So let's open a new terminal. 07:02.670 --> 07:06.360 Let's go to the workspace and let's build it. 07:11.610 --> 07:14.130 Now we can finally start using our interface. 07:14.460 --> 07:26.250 So here from the Arduino bot messages and from the action folder, let's import the Fibonacci interface. 07:26.250 --> 07:30.360 And now let's use this one to initialize the action server object. 07:30.360 --> 07:36.180 So here in the constructor of the action server object, let's say that this action server is going 07:36.180 --> 07:39.570 to use the Fibonacci interface. 07:39.570 --> 07:43.440 And also let's assign a name to the action server. 07:43.560 --> 07:51.690 Let's call this one for example, Fibonacci, and this is the name that other Ros two nodes can use 07:51.720 --> 07:54.870 in order to send goals to the action server. 07:54.870 --> 08:01.710 And so in order to calculate the Fibonacci sequence, finally for the constructor, we also have to 08:01.710 --> 08:08.310 define the name of the function that this server will execute whenever a new goal message is received, 08:08.340 --> 08:13.750 which is the function that contains the logic for the calculation of the Fibonacci sequence itself. 08:14.310 --> 08:17.100 We call this the call callback function. 08:17.100 --> 08:26.190 So let's use the goal callback function and we are going to define this function still within the simple 08:26.190 --> 08:26.790 action server. 08:26.820 --> 08:34.020 So as a member of the Simple Action server class, with this we have instantiated and initialized a 08:34.020 --> 08:41.730 new action server that is called Fibonacci, which uses a message interface called Fibonacci that is 08:41.730 --> 08:44.550 defined in the Arduino board messages package. 08:45.210 --> 08:45.930 Next. 08:45.930 --> 08:49.140 Still in the constructor, let's print an informative message. 08:49.500 --> 09:02.280 So with the get logger function, let's print an informative message that says Starting the server. 09:02.370 --> 09:06.990 And now let's go on and also define the callback function. 09:06.990 --> 09:13.800 So the goal callback function as a member of the simple action server class. 09:14.520 --> 09:16.440 As this function will be executed. 09:16.440 --> 09:23.120 Whenever a client sends a new goal to an action server, it receives the goal message as an input. 09:23.130 --> 09:27.810 So the one that we defined in the Fibonacci action interface. 09:28.020 --> 09:32.250 And so let's call this variable goal Endl. 09:33.180 --> 09:37.440 So when this function is called, let's start by printing an informative message. 09:38.100 --> 09:42.210 So still with the get logger function. 09:42.720 --> 09:45.060 Let's print an informative message. 09:45.060 --> 09:54.030 And this message says received call request with order. 09:54.210 --> 09:57.920 And then let's print the order that was just received. 09:57.930 --> 10:04.340 And so basically we can display the order by accessing the goal handle. 10:04.380 --> 10:11.520 And from this one, let's access to the request and then to the order. 10:12.270 --> 10:18.570 Next, let's create a new feedback message that will be sent periodically to the client, informing 10:18.570 --> 10:22.260 it about the progress of the Fibonacci sequence calculation. 10:22.620 --> 10:32.880 So let's call this one feedback message, and this is from the Fibonacci interface, an instance of 10:32.980 --> 10:35.470 the feedback message feedback. 10:36.580 --> 10:37.210 Okay. 10:37.210 --> 10:43.390 And we can already initialize it with the first two numbers that always make up a Fibonacci sequence. 10:43.390 --> 10:53.650 So let's access to the feedback message and to the partial sequence and let's initialize the sequence 10:53.650 --> 10:59.350 with the numbers zero and one that always are present within the Fibonacci sequence. 10:59.930 --> 11:04.320 And now we can implement the actual logic for the Fibonacci sequence calculation. 11:04.340 --> 11:08.150 So let's create a for loop that goes from one. 11:08.150 --> 11:12.110 So let's create a new variable E in range. 11:12.680 --> 11:16.250 And so this goes from one until the requested order. 11:16.670 --> 11:22.370 So the goal Endl request order. 11:23.210 --> 11:28.070 So this for loop goes from one to the requested order of the Fibonacci sequence. 11:28.250 --> 11:33.380 And then at each iteration of this loop, let's add a new element to the partial sequence. 11:33.380 --> 11:41.180 So to the feedback message, to the partial sequence, which is an array. 11:41.210 --> 11:49.670 Let's append a new element, and this new element is given by the sum with the last element that is 11:49.670 --> 11:51.350 present in the partial sequence. 11:51.680 --> 11:55.070 So let's take again the partial sequence. 11:56.440 --> 12:00.100 Here and let's access to the last element. 12:00.100 --> 12:06.220 So to the element, to the position I and let's add to this one the element at the previous position. 12:06.220 --> 12:08.170 So the second last one position. 12:08.380 --> 12:15.880 So still to the partial sequence, let's access to the element I minus one at each iteration. 12:15.880 --> 12:18.880 Let's also print an informative message in the terminal. 12:20.140 --> 12:31.270 So with the get logger function, let's print an informative message with the current feedback. 12:31.270 --> 12:33.580 So feedback. 12:34.090 --> 12:36.460 And then let's print the partial sequence. 12:36.970 --> 12:44.110 So let's format this string in order to print the feedback message partial sequence. 12:44.110 --> 12:49.540 So in order to print the Fibonacci sequence that we have calculated up to this moment, so up to this 12:49.540 --> 12:50.650 loop iteration. 12:51.680 --> 12:59.180 Then by using the goal and object, we can send this feedback message also to the client, informing 12:59.180 --> 13:01.310 it about the progress of the server. 13:01.760 --> 13:09.740 To do so, let's use the function, publish feedback of the goal and object. 13:09.740 --> 13:13.070 And to this one we pass the feedback message. 13:14.150 --> 13:20.120 Finally to simulate that the action server is performing as low and resource intensive operation. 13:20.120 --> 13:22.940 So an operation that takes some time to complete. 13:22.970 --> 13:25.040 Let's add a slip to the loop. 13:25.040 --> 13:28.520 And so this will pause the execution of the script for a second. 13:28.520 --> 13:33.140 So at each iteration of this loop, let's pause the execution for one second. 13:33.620 --> 13:38.120 To do so, let's import the Python time library. 13:38.450 --> 13:40.090 And now from this library. 13:40.100 --> 13:47.750 So from the time library, let's use the slip function to make this script slip for one second and then 13:47.750 --> 13:52.910 it will continue with the execution of the for loop once the loop is finished. 13:52.910 --> 13:58.550 So the action server will have calculated all the numbers in the Fibonacci sequence and also will have 13:58.550 --> 14:02.990 sent a feedback message for each of the elements that it has calculated. 14:03.080 --> 14:08.270 And so now we can conclude the action and return a result message to the client. 14:08.510 --> 14:15.120 So let's use the goal and goal variable and let's set this one to succeed. 14:15.930 --> 14:22.590 And then let's also create a new result message as an instance of the Fibonacci interface. 14:23.610 --> 14:27.510 And so of the result message that we declared in this interface. 14:27.510 --> 14:31.620 And now so this is the result variable. 14:31.920 --> 14:37.770 And now let's set to the result variable to the sequence. 14:37.770 --> 14:44.670 Let's set basically the full Fibonacci sequence and so we can set this one equal to the feedback message, 14:44.670 --> 14:45.990 partial sequence. 14:45.990 --> 14:52.800 Since up to this point, the partial sequence already contains all the elements that makes up the Fibonacci 14:52.800 --> 14:56.670 sequence up to the requested order so we can set this one. 14:56.760 --> 15:02.790 The sequence of the result equal to the last partial sequence that is in the feedback message. 15:03.030 --> 15:12.210 And so let's return exactly this result message to the client which requested the execution of these 15:12.240 --> 15:13.230 actions. 15:13.860 --> 15:16.260 With this the simple action server node. 15:16.380 --> 15:20.730 So this class is completed and now we can define the main function. 15:27.840 --> 15:34.560 And this calls the function main that we can define here. 15:35.940 --> 15:37.980 So let's define the function main. 15:37.980 --> 15:45.420 And now within this function, let's start by initializing ros2 with rcl pi init. 15:45.840 --> 15:49.320 Then let's create a new instance of the simple action server. 15:49.560 --> 15:57.870 So let's call this variable simple action server as an instance of the simple action server and let's 15:57.870 --> 15:59.130 keep this node up and running. 15:59.130 --> 16:03.590 So let's keep the action server up and running ready to receive new goals. 16:03.600 --> 16:11.490 So let's use the Pi spin function to spin the simple action server. 16:11.490 --> 16:18.840 And as usual, when we press control C, let's make the shutdown of this node so simple Action server. 16:18.840 --> 16:27.750 Let's destroy the node, destroy the node and also let's make the Pi shut down. 16:27.750 --> 16:29.970 So let's call this shutdown of this node. 16:31.140 --> 16:38.910 As usual, in order to compile and install this script, we need to add it into the setup.py file. 16:38.940 --> 16:43.200 So here we need to add a new line in the console script. 16:43.200 --> 16:50.700 So in the entry points so we can copy the one for the simple service client and let's call this one. 16:51.410 --> 17:00.440 So the new executable Simple action server and its source code is still in the Arduino, but by examples 17:00.470 --> 17:06.260 this time is in the simple action server. 17:06.260 --> 17:10.070 And still from this script we want to execute the main function. 17:10.520 --> 17:16.880 Now we can save also this file and we just need to compile our workspace again so that the new node 17:16.880 --> 17:18.620 becomes an executable. 17:18.980 --> 17:26.300 So let's open a new terminal, go to the workspace and let's build it with the command. 17:26.300 --> 17:27.230 Click on Build. 17:27.620 --> 17:33.560 Once the build is succeeded, we can open a new window of the terminal and finally we can start our 17:33.560 --> 17:34.610 action server. 17:34.910 --> 17:42.050 So let's source the file setup dot bash so that the Arduino Pi example package is recognized. 17:42.230 --> 17:48.200 And now from this package, so from the Arduino Pi examples. 17:48.200 --> 17:53.610 So if we press tab twice now we can see that there is the simple action server available. 17:53.790 --> 18:00.360 So let's start this one, the simple action server, let's press enter and we get the confirmation that 18:00.360 --> 18:06.390 the action server is running from the terminal so we can see that the simple action server is saying 18:06.420 --> 18:14.100 starting the server and also we can actually double check it by opening a new terminal. 18:14.250 --> 18:20.040 And here we can use the command Ros2 action list. 18:20.040 --> 18:22.050 So let's press enter. 18:22.050 --> 18:28.080 And since we have started only one node, so the one that creates and starts the Fibonacci action server, 18:28.110 --> 18:32.580 this is also the only action server that is currently available in Ros two. 18:32.610 --> 18:37.080 So this one if we search the workspace also in this new terminal. 18:37.080 --> 18:39.330 So let's source the file setup dot bash. 18:39.480 --> 18:48.960 We can have additional information about this action server using the command Ros2 action info followed 18:48.960 --> 18:57.080 by the name of the action, which is the Fibonacci, followed by the minus D flag in order to show also 18:57.080 --> 18:58.460 the message interface. 18:58.460 --> 19:01.880 So the type of the interface that this action is using. 19:02.000 --> 19:08.540 So let's press enter and currently we can see that for this action server there is only one node that 19:08.540 --> 19:10.100 is interacting with it. 19:10.250 --> 19:16.610 So here that is the simple action server node that actually creates this action server. 19:16.610 --> 19:24.920 And also we can see that this action server is using the interface Fibonacci as declared in the Arduino 19:24.920 --> 19:26.120 board messages. 19:26.720 --> 19:32.870 At this moment we can see that there are no clients, so actually there is nobody that is interested 19:32.870 --> 19:38.510 in the functionalities of this server and we can send a new goal to this server. 19:38.510 --> 19:44.510 So to the Fibonacci server in order to see how it works, to send a goal to an action server, we can 19:44.510 --> 19:55.050 use the command Ros2 action and then send goal followed by the name of the action, which is the Fibonacci, 19:55.080 --> 19:56.190 the action server. 19:56.220 --> 20:03.810 Then if we press tab twice we can see that the Ros two autocompletion is able to detect that we need 20:03.810 --> 20:07.140 an interface of type Arduino board messages Fibonacci. 20:08.040 --> 20:12.090 So let's use this interface to send a new goal to the action server. 20:12.120 --> 20:13.740 Then let's use double quote. 20:14.260 --> 20:16.000 And then let's set the order. 20:16.000 --> 20:17.320 So let's press tab. 20:17.590 --> 20:24.010 And so this has inserted an empty prototype of the goal message that we are going to send to the Fibonacci 20:24.010 --> 20:24.970 action server. 20:25.180 --> 20:27.750 So, for example, let's set the order to ten. 20:27.760 --> 20:33.010 So we are asking the action server to calculate the Fibonacci sequence up to the order ten. 20:33.710 --> 20:41.570 Let's also use the flag minus F in order to print the feedback messages that the server will send in 20:41.570 --> 20:42.500 this same terminal. 20:42.500 --> 20:44.870 So minus F stands for feedback. 20:45.170 --> 20:51.320 So let's press enter and as soon as we send this goal, we can see how the action server informs us 20:51.320 --> 20:57.350 that it has received a new goal and also that it starts processing the Fibonacci sequence element by 20:57.350 --> 21:00.560 element up to the order ten for each number. 21:00.560 --> 21:05.030 Also, we can see that for each new element that the server is adding to the sequence. 21:05.060 --> 21:10.280 It also sending a feedback message that informs us about the progress of the goal. 21:10.610 --> 21:16.490 And finally, once the desired order is reached, the action server also returns a result message. 21:16.490 --> 21:19.490 So this one here with default. 21:19.520 --> 21:22.580 So the complete sequence up to the desired order. 21:22.580 --> 21:24.260 So up to the order ten.