WEBVTT 00:00.050 --> 00:05.990 Now that you know what a node is, let's create a Python node in our Python package. 00:05.990 --> 00:08.510 So we will first write a very minimal code. 00:08.510 --> 00:11.030 Here we will install and run the node. 00:11.030 --> 00:16.160 And then in the next lesson we will use object oriented programming to improve the node. 00:16.160 --> 00:21.620 And from that we will have a code template that we can use for any future node that you create. 00:21.620 --> 00:22.940 So let's get started. 00:22.940 --> 00:28.730 First let's go back to our workspace in the source folder here. 00:28.730 --> 00:31.190 And then in the package. 00:31.610 --> 00:35.870 So my Python package okay what do we have here. 00:35.900 --> 00:37.550 Well we have several files and folders. 00:37.550 --> 00:42.380 And if you remember we have a folder that has the same name as the package. 00:42.380 --> 00:44.840 So we go inside that one. 00:45.350 --> 00:56.000 So now you see we are in my pi pkg inside my pi pkg inside the source folder of the ros2 workspace. 00:56.000 --> 00:58.640 And we have here the Init.py. 00:58.670 --> 01:01.530 So we will create a new file right here. 01:01.860 --> 01:02.610 Let's do touch. 01:02.610 --> 01:05.610 And let's name my first node. 01:05.640 --> 01:07.170 Dot p y. 01:07.950 --> 01:08.220 Great. 01:08.220 --> 01:10.350 So now we have the file that we can edit. 01:10.350 --> 01:11.880 And I'm going to use VSCode. 01:11.880 --> 01:19.530 So to open VSCode you see I have closed it previously I'm going to go back to the source folder of my 01:19.530 --> 01:20.280 workspace. 01:20.310 --> 01:20.850 Okay. 01:20.850 --> 01:23.220 And then I'm going to do code dot. 01:23.220 --> 01:26.400 So I'm going to open VSCode from that folder only. 01:28.800 --> 01:29.400 Great. 01:29.400 --> 01:33.660 And we can find here the file is going to be here. 01:33.660 --> 01:35.490 So let's start to write the code. 01:35.490 --> 01:39.180 First we will add the interpreter line for Python. 01:39.210 --> 01:47.460 So like that user bin and and then Python three. 01:47.490 --> 01:49.530 Make sure you don't make any typo here okay. 01:49.560 --> 01:52.950 So this line is going to say that we use Python three just in case. 01:52.980 --> 01:56.100 For example you make an executable and you run it like that. 01:56.130 --> 02:00.270 It's going to use Python three to interpret and execute the code. 02:00.270 --> 02:06.540 And then the first thing we will do is to import the RCL py library. 02:06.570 --> 02:06.780 Okay. 02:06.810 --> 02:10.560 So that's basically our CLP is the Ros2 library for Python. 02:10.560 --> 02:13.080 You will need that in all your Python nodes. 02:13.080 --> 02:17.910 And as you can see here I have the auto completion. 02:18.240 --> 02:20.430 I can press tab for the auto completion. 02:20.430 --> 02:25.350 If you don't have this in VSCode, it's because you haven't correctly set up the extension. 02:25.350 --> 02:30.780 So you go back to the extensions here Ros extension and you make sure it's correctly installed. 02:30.780 --> 02:35.730 So the Ros extension from Microsoft you might need to restart VSCode okay. 02:35.760 --> 02:37.260 Make sure it's installed. 02:37.260 --> 02:38.970 And then you should have the auto completion. 02:38.970 --> 02:39.330 Great. 02:39.330 --> 02:40.980 So we import our CLP. 02:40.980 --> 02:49.170 And then we also import from our CLP dot node import node. 02:49.170 --> 02:50.790 So we import the node class. 02:50.790 --> 02:52.290 So n uppercase. 02:52.290 --> 02:56.550 Here we import the node class from CLP node okay. 02:56.580 --> 02:58.050 That's all the imports that we need. 02:58.080 --> 03:02.680 For now let's create a main function. 03:02.710 --> 03:09.370 So I create a div main and let's put some optional arguments that we can pass to the main function. 03:09.370 --> 03:11.320 And let's name this args. 03:11.500 --> 03:12.280 Okay. 03:12.400 --> 03:14.890 And what do we do inside this main function. 03:14.890 --> 03:17.860 So what do we do inside the Ros2 program. 03:17.890 --> 03:27.730 The first thing that you will do the first line is going to be rcl py dot init. 03:27.970 --> 03:29.890 And you can pass arguments. 03:29.890 --> 03:32.590 So args is equal to x. 03:32.590 --> 03:34.870 So it has a args argument okay. 03:34.900 --> 03:37.000 And you can give the arguments that you get from the main. 03:37.000 --> 03:43.120 So that's the first thing you will do in any ros2 programs you need to initialize Ros2. 03:43.150 --> 03:47.620 So it's going to initialize Ros2 communications and all the stuff that you need. 03:47.650 --> 03:50.350 Then to create and use nodes. 03:50.350 --> 03:52.030 Then we're going to do some stuff. 03:52.030 --> 03:59.230 And the last line that you will write is RCL pi dot shutdown okay. 03:59.260 --> 04:02.990 And you see here again I use the auto completion. 04:02.990 --> 04:05.690 So use the auto completion as much as possible. 04:05.690 --> 04:08.000 I really recommend you to use something. 04:08.000 --> 04:12.710 So if you don't use VSCode, use something else that has auto completion for Ros2. 04:12.740 --> 04:14.360 That's going to be super useful. 04:14.390 --> 04:14.720 Great. 04:14.720 --> 04:19.460 So CLP init and then at the end CLP dot shutdown. 04:19.460 --> 04:22.940 Now that we have this we can create a node. 04:22.940 --> 04:26.240 So let's do node is equal to node. 04:26.240 --> 04:29.420 So we use the node class here okay. 04:29.450 --> 04:31.250 And we need to give it a name. 04:31.250 --> 04:33.800 So for example let's name it Pi test. 04:33.800 --> 04:35.270 That's going to be our first node. 04:35.300 --> 04:42.170 Now you can note one thing is that we actually create a node inside the Python file okay. 04:42.170 --> 04:45.290 So the Python file itself is not really the node. 04:45.290 --> 04:47.870 The node is inside the file. 04:47.900 --> 04:48.410 All right. 04:48.410 --> 04:52.280 And that's the minimum code for a node. 04:52.280 --> 04:53.660 So you just create a node. 04:53.660 --> 04:55.070 You initialize Ros2 communication. 04:55.070 --> 04:56.600 You create a node and you shut down. 04:56.600 --> 04:59.060 Now that's not going to do anything if we test it. 04:59.060 --> 05:01.820 So let's add a log here. 05:01.850 --> 05:03.620 Let's do node dot. 05:03.650 --> 05:05.810 So you see that inside the node. 05:05.840 --> 05:13.580 Thanks to the all the functionalities from the node class from our CLP we can do node dot get logger. 05:13.580 --> 05:22.430 So we get the logger functionality and then.info for example with let's say hello world. 05:22.460 --> 05:24.710 That's going to be our Hello World program. 05:24.710 --> 05:31.910 And now we have a node that will well be initialized and then print something on the terminal. 05:32.210 --> 05:36.260 So that's it I'm just going to add here if name. 05:36.260 --> 05:44.480 So double underscore name is equal to and then double underscore main double underscore. 05:44.660 --> 05:47.030 And let's call the main function. 05:47.060 --> 05:47.270 Okay. 05:47.300 --> 05:48.590 That's just useful. 05:48.590 --> 05:53.420 If you want to run the program directly from the terminal then that's going to call the main function 05:53.420 --> 05:54.920 automatically for you. 05:54.950 --> 05:55.310 Okay. 05:55.340 --> 05:56.690 And that's what we're going to do right now. 05:56.690 --> 05:58.700 So I add this bit of code. 05:58.740 --> 06:02.940 Now it's very important that you save the files. 06:02.970 --> 06:08.520 Okay, I see lots of errors of people starting with Ros2 and they forget to save the file. 06:08.520 --> 06:12.300 As you can see here we have a dot, a big dot. 06:12.330 --> 06:15.480 If I save with Ctrl s now it's a cross. 06:15.510 --> 06:20.430 Okay, so that's an easy way to see if you have saved the files or not on VSCode. 06:20.430 --> 06:22.470 So make sure you save that file. 06:22.470 --> 06:24.120 Then let's go back to the terminal. 06:24.120 --> 06:27.390 And let's go back to where the file was. 06:28.440 --> 06:31.020 My Python package okay. 06:31.020 --> 06:37.470 And what you can run it with the Python three command directly or make it executable. 06:37.470 --> 06:47.910 For example with chmod plus x my first node you see now it is executable and I can run my first node 06:47.910 --> 06:48.630 directly. 06:48.630 --> 06:50.130 So let's see what we have. 06:50.160 --> 06:53.430 I press enter and you see we have hello world. 06:53.430 --> 06:54.840 So it correctly worked. 06:55.530 --> 06:59.440 You see we have info that corresponds to the info log level. 06:59.470 --> 07:04.750 Here then we have a timestamp and then we have the name of the node. 07:04.750 --> 07:06.250 So pi test. 07:06.280 --> 07:07.180 Why pi test? 07:07.180 --> 07:09.460 Because that's what we have defined here. 07:09.490 --> 07:10.120 Okay. 07:10.210 --> 07:12.970 When we create the node we give it a name. 07:13.000 --> 07:13.330 All right. 07:13.360 --> 07:14.410 So that's what you see. 07:14.410 --> 07:21.190 But what you see also is if I run it again we print the log and then we exit from the program. 07:21.190 --> 07:25.210 And that's quite normal because here we just initialize Ross to communication. 07:25.300 --> 07:29.350 We create a node, we print something and then we shut down everything. 07:29.350 --> 07:35.890 Now a quite common thing to do with a node is to actually keep it alive so it can process more stuff. 07:35.920 --> 07:36.160 Okay. 07:36.190 --> 07:39.940 And you just want to keep it alive and stop it when you want. 07:39.970 --> 07:40.960 How to do this? 07:40.960 --> 07:50.140 Well, after we create the node before we shutdown, of course we are going to do RCL pi dot spin. 07:50.170 --> 07:56.260 And as a parameter we are going to provide the node that we have just created okay. 07:56.260 --> 08:01.760 So we create the node and then we pass it to the spin functionality and the spin. 08:01.760 --> 08:04.400 So spin is very important mechanism in Ros. 08:04.400 --> 08:06.950 And we're going to come back to this a lot during this course. 08:06.950 --> 08:12.770 But for now you just have to know that the spin is going to keep the node alive until you press Ctrl 08:12.800 --> 08:13.040 C. 08:13.070 --> 08:17.480 So let's save that and let's start again. 08:18.140 --> 08:20.030 And you can see that now we have Hello world. 08:20.030 --> 08:23.870 But the node is still hanging there okay. 08:23.900 --> 08:26.780 If I press enter the node is still hanging there. 08:26.780 --> 08:28.040 If I press Ctrl c. 08:28.070 --> 08:31.040 Now we exit from the node. 08:31.040 --> 08:32.750 So everything is going to be shut down. 08:32.750 --> 08:35.930 The node is going to be shut down and we exit from the program. 08:35.960 --> 08:36.470 All right. 08:36.470 --> 08:38.960 So I'm going to keep this like this here. 08:38.960 --> 08:41.210 And I'm going to explain more about it a bit later. 08:41.240 --> 08:44.840 Now what we have done so far is we have a file that's a valid file. 08:44.840 --> 08:49.190 We have run the file from where we created it directly. 08:49.190 --> 08:54.470 But now what we want to do actually when we create a new file like this is we want to install it, we 08:54.470 --> 08:59.510 want to install it and create an executable that we can start then with the ros2. 08:59.540 --> 09:00.320 Command line. 09:00.320 --> 09:01.820 And that's going to be super useful. 09:01.820 --> 09:05.810 For example, later we can also start it from a launch file, etc.. 09:05.810 --> 09:11.480 So even if you can run the Python program like this directly from the source folder here of the workspace, 09:11.480 --> 09:15.200 we're going to install the node and how to install the node. 09:15.200 --> 09:21.980 Well you will just go inside your Python package to the setup.py inside this file. 09:21.980 --> 09:23.720 Here you see lots of stuff. 09:23.720 --> 09:28.100 But at the end you see entrypoints with console scripts. 09:28.100 --> 09:29.630 And that's an array. 09:29.660 --> 09:30.650 That's a list here. 09:30.650 --> 09:36.410 So you go inside this, you open double quotes and we are going to give the instructions to create a 09:36.410 --> 09:38.030 new executable. 09:38.210 --> 09:39.350 So I'm going to create it. 09:39.380 --> 09:40.250 We're going to run it. 09:40.250 --> 09:42.860 And then I'm going to come back and explain a bit more about it. 09:42.860 --> 09:47.660 So let's create an executable which name is py node. 09:47.660 --> 09:50.000 So that is something that I choose. 09:50.000 --> 09:53.390 Then I will put a space equal space. 09:53.390 --> 09:56.420 And then I need to provide basically the path. 09:56.450 --> 10:00.000 So the relative path to the file here. 10:00.270 --> 10:02.730 So we need to go to my pi pkg. 10:02.730 --> 10:05.160 So usually there's going to be the package name. 10:05.730 --> 10:15.240 So package name and then dot the file name here it's my first node dot pi my first node. 10:15.240 --> 10:18.270 But I don't provide the pi extension okay. 10:18.300 --> 10:21.240 So just my first node okay. 10:21.270 --> 10:24.750 Package dot file without the extension. 10:24.870 --> 10:26.310 And then we have a colon. 10:26.310 --> 10:30.960 And we need to provide the name of the function that we want to call. 10:30.960 --> 10:37.200 So when we start this we are going to call a function from that program what function we want to call. 10:37.200 --> 10:38.940 Well that's going to be the main function. 10:38.940 --> 10:42.120 So we write main just like that. 10:42.120 --> 10:44.160 No parentheses nothing okay. 10:44.190 --> 10:52.140 So you choose a name for the executable and then package dot file name colon function to call. 10:52.200 --> 10:53.130 And that's it. 10:53.160 --> 10:56.640 If you want to add more executables you will need to add a comma. 10:56.670 --> 10:59.530 Go to a new line and then do the same thing again. 10:59.560 --> 11:01.900 Okay, but for now we only have one. 11:01.900 --> 11:04.180 So let's save this file. 11:04.180 --> 11:05.200 Very important. 11:05.230 --> 11:06.700 You save all the files. 11:06.910 --> 11:11.200 Let's go back to the terminal and let's go to. 11:11.230 --> 11:14.980 So let's go to the Ros2 workspace. 11:15.010 --> 11:16.030 Once again. 11:16.030 --> 11:17.230 Very important. 11:17.230 --> 11:20.380 You don't build just anywhere. 11:20.380 --> 11:24.220 You only built in the Ros2 workspace folder. 11:24.220 --> 11:26.200 That's super, super important. 11:26.200 --> 11:27.940 So we are here I can do. 11:27.970 --> 11:29.110 So let's do clear here. 11:29.110 --> 11:35.650 And I can do call on build now because I have two packages and I only want to build the Python one. 11:35.650 --> 11:39.760 I'm going to use packages select. 11:39.760 --> 11:41.020 So it's not really important. 11:41.020 --> 11:42.220 You could build the two packages. 11:42.220 --> 11:44.380 But here let's do things in a clean way. 11:44.380 --> 11:51.040 So packages select and then my pi pkg okay. 11:51.040 --> 11:53.680 So we build the Python package. 11:53.680 --> 11:58.210 And now what's going to happen is that you just gave an instruction to create an executable. 11:58.210 --> 12:03.070 So inside the install folder here. 12:03.220 --> 12:06.490 Well you can try to browse inside and maybe find the executable. 12:06.490 --> 12:07.390 It doesn't really matter. 12:07.390 --> 12:13.720 But basically you know that this executable here pi node is going to be created inside the install folder. 12:13.750 --> 12:17.530 And it doesn't really matter where because we don't need to go inside this. 12:17.530 --> 12:21.880 We can use the Ros2 command line tool directly to run the executable. 12:21.970 --> 12:22.600 Okay. 12:23.380 --> 12:26.290 So for example let's say I'm in my home directory. 12:26.290 --> 12:28.150 Well you could do that from wherever. 12:28.150 --> 12:29.350 And I'm still going to here. 12:29.350 --> 12:31.660 I'm still going to source the bashrc. 12:31.660 --> 12:37.060 So you could do complete path with tilde slash dot bash RC. 12:37.090 --> 12:37.990 Why is that? 12:37.990 --> 12:44.260 Because well, I have just created something new in my workspace and because I have created something 12:44.260 --> 12:47.350 new, I'm going to source my workspace. 12:47.380 --> 12:47.530 Okay. 12:47.560 --> 12:52.660 Just to be sure that I have the latest updates and how to source the workspace. 12:52.660 --> 12:58.730 Well, you could source the setup bash script inside the install folder, but you can also source the 12:58.730 --> 13:03.020 bashrc because, well, we already have the line to do this inside the bashrc. 13:03.050 --> 13:03.680 Okay. 13:03.680 --> 13:09.140 So just make sure that you choose the workspace if you have created something new. 13:09.170 --> 13:09.410 Okay. 13:09.440 --> 13:10.370 In a terminal. 13:10.400 --> 13:14.840 Or you could open a new terminal and then everything is done for you automatically. 13:14.840 --> 13:20.120 So for example we source that and then I can start the node with Ros2 run. 13:20.150 --> 13:23.810 I will need to first provide the package name. 13:24.020 --> 13:26.660 The package name is my pi pkg. 13:26.720 --> 13:28.400 You see I can press the auto completion. 13:28.430 --> 13:29.210 It should be found. 13:29.210 --> 13:34.460 If it's not found here then you have a problem already and you need to go back and make sure that you've 13:34.460 --> 13:36.800 done everything and then well. 13:36.800 --> 13:38.900 So I do roster package name. 13:38.900 --> 13:42.170 And then I need to provide the executable name. 13:42.170 --> 13:44.030 What is the executable name. 13:44.030 --> 13:49.130 Well once again the executable name is what we have created here in the setup.py. 13:49.130 --> 13:51.800 So it's called here pi node. 13:52.640 --> 13:54.800 So pi node. 13:54.800 --> 13:56.770 And I don't even need to type everything. 13:56.800 --> 13:58.180 I can press Tab here. 13:58.210 --> 13:58.630 Okay. 13:58.660 --> 13:59.800 It's going to be found. 13:59.830 --> 14:04.960 I press enter and you can see it is currently working. 14:04.960 --> 14:06.760 So now I have created a node. 14:06.790 --> 14:12.940 I have installed it and I can run it from anywhere using the Ros to run command line tool. 14:12.940 --> 14:15.070 And now I can do ctrl C to stop. 14:15.070 --> 14:16.480 So we have a keyboard interrupt. 14:16.480 --> 14:18.790 But you don't need to really worry about that. 14:18.820 --> 14:19.330 Okay. 14:19.330 --> 14:24.220 And I'm just going to come back to one very important thing that you need to make sure to understand 14:24.250 --> 14:25.030 is that. 14:25.030 --> 14:27.070 So we have the executable name here. 14:27.100 --> 14:31.300 The executable name is what's created after you install the node here. 14:31.330 --> 14:32.890 So let's pick node here. 14:33.190 --> 14:36.280 But then we also have pytest. 14:36.310 --> 14:38.920 Pytest is the node name. 14:38.920 --> 14:43.870 And the node name is what you have defined here inside the code. 14:43.900 --> 14:44.170 Okay. 14:44.200 --> 14:45.850 So that's two different things. 14:45.850 --> 14:51.610 The executable name here and the node name are different things. 14:51.610 --> 14:54.850 And then also we have my first node.py. 14:54.880 --> 14:56.730 That's the file name. 14:56.760 --> 14:56.910 Okay. 14:56.940 --> 14:58.560 So we have three different things here. 14:58.560 --> 15:02.040 We have the node name that we create inside the file. 15:02.070 --> 15:03.630 We have the file name. 15:03.630 --> 15:09.930 And then we have the executable name that we create so that we can use with Ros to run. 15:09.960 --> 15:11.730 Okay three different things. 15:11.730 --> 15:16.770 And here I used different names for all three just to show you that there are different things. 15:16.770 --> 15:18.630 But sometimes you will see the same. 15:18.630 --> 15:24.810 For example, if you create a temperature sensor file, you might name it temperature sensor dot p y 15:24.810 --> 15:28.500 and then the node name might be temperature sensor. 15:28.500 --> 15:32.460 And the executable name also might be temperature sensor. 15:32.460 --> 15:37.200 But you need to be aware that those are three different things okay. 15:37.230 --> 15:39.570 And I'm going to come back to this also later. 15:39.570 --> 15:40.800 But for now well, great. 15:40.800 --> 15:45.240 You've made a lot of progress already because you can create a file here. 15:45.240 --> 15:48.240 You can create a file to write a node. 15:48.240 --> 15:51.390 You can write a basic version of a node. 15:51.390 --> 15:56.160 You can install that node and run that node from the terminal.