WEBVTT 00:00.080 --> 00:03.830 And now let's see how to make your python program retry. 00:03.860 --> 00:07.220 To connect to serial after it has failed. 00:07.430 --> 00:09.140 That can be super useful. 00:09.380 --> 00:15.470 So basically when you start the program, so any program where you're going to connect to the Arduino 00:15.500 --> 00:21.950 with serial communication, you can choose what you want to do if the communication is not successfully 00:21.950 --> 00:22.760 working. 00:22.760 --> 00:25.130 So you can leave it like that, of course. 00:25.130 --> 00:28.400 And if it's not working, you're just going to get an error. 00:28.400 --> 00:31.010 And then you need to start the program again. 00:31.010 --> 00:32.660 Or you can add a mechanism. 00:32.660 --> 00:32.940 Okay. 00:32.960 --> 00:38.570 Just on that line here to try again if it can't connect. 00:38.570 --> 00:40.970 And that's what I'm going to show you here. 00:40.970 --> 00:43.370 So how to do that? 00:43.370 --> 00:48.230 Well, first, so I'm going to unplug my Arduino so the Arduino is not connected. 00:48.230 --> 00:50.810 Let's see again, what error do we have? 00:50.840 --> 00:54.020 We have a serial exception here. 00:54.140 --> 00:54.560 Okay. 00:54.560 --> 00:59.030 So we are going to get this exception. 00:59.180 --> 00:59.690 All right. 00:59.690 --> 01:03.090 So I'm going to do try with this. 01:03.480 --> 01:06.330 And then except. 01:06.330 --> 01:12.180 And the exception is serial dot serial exception. 01:12.180 --> 01:12.930 You can use that. 01:12.930 --> 01:13.380 Okay. 01:13.380 --> 01:19.230 So if you have a serial exception, which means that you have a problem when you connect, which can 01:19.230 --> 01:25.770 be, for example, that the board is not connected or that the port is already busy, then instead of 01:25.890 --> 01:31.200 exiting the program right now, you're going to go inside this code to handle the exception. 01:31.200 --> 01:36.960 And so what you want to do is that if you reach that, you want to go back to here, and if you want 01:36.960 --> 01:40.830 to go back to here, then I'm going to use a while loop. 01:40.830 --> 01:49.530 So let's do while true, I'm going to put that inside the while loop, of course, with a colon here. 01:49.650 --> 01:58.050 So while true means that first we're going to enter this anyway, we're going to execute this code if 01:58.050 --> 02:03.420 this is successful, which means that we don't have the exception, then in that case, what we want 02:03.420 --> 02:06.690 to do is we want to break out of the loop. 02:06.780 --> 02:07.260 Okay. 02:07.260 --> 02:08.850 So I'm going to add break. 02:08.850 --> 02:15.450 So if this is successful, we directly go after the while loop and we go to time.sleep. 02:15.870 --> 02:20.310 And if it is not successful, we are going to get the exception. 02:20.310 --> 02:22.980 And in the exception, well, let's print something. 02:22.980 --> 02:34.530 Let's say print could not connect to serial trying again. 02:35.520 --> 02:41.640 And let's add, let's say time dot sleep one. 02:41.640 --> 02:50.160 So if it's not working, we are going to print something, sleep for one second and then come back to 02:50.160 --> 02:51.480 the beginning of the loop. 02:51.480 --> 02:54.870 So we try again every one second. 02:55.080 --> 02:55.560 Okay. 02:56.310 --> 03:03.290 I'm just going to add another print here so we can know directly after we have successfully connected 03:03.290 --> 03:13.580 that the connection is okay, so let's say success fully connected to Serial. 03:15.950 --> 03:16.370 Okay? 03:16.370 --> 03:18.950 And that should be it. 03:18.950 --> 03:22.250 So now I'm going to run this code. 03:22.310 --> 03:28.730 The Arduino is still disconnected, so you can see what we're going to have is could not connect to 03:29.150 --> 03:30.050 trying again. 03:30.050 --> 03:32.570 And now I'm going to connect the Arduino. 03:32.600 --> 03:38.390 The program is still running and you can see successfully connected to serial. 03:38.480 --> 03:39.110 Serial. 03:39.140 --> 03:39.530 Okay. 03:39.530 --> 03:42.320 And then we have the application which is starting. 03:42.320 --> 03:45.320 I press Ctrl C to kill the application. 03:46.190 --> 03:52.880 Okay, so with this code, it's going to try again and again and again until the connection can be established 03:52.880 --> 03:55.070 and that can be very useful. 03:55.070 --> 03:58.220 We are going to use that actually in the final project of this course. 03:58.220 --> 04:01.160 I'm not going to use it in every activity. 04:01.190 --> 04:03.890 Okay, because that adds a bit of code. 04:03.890 --> 04:07.280 If we want to just focus on 1 or 2 functionalities. 04:07.280 --> 04:13.190 But for the final project we are going to use that and actually as an improvement that I'm not going 04:13.190 --> 04:15.590 to code here, but you could try to do that. 04:15.620 --> 04:18.770 You could try to add a maximum number of tries. 04:18.800 --> 04:25.790 Okay, let's say you want to try for maximum ten times, which means that after 10s the problem is going 04:25.790 --> 04:26.750 to exit anyway. 04:26.750 --> 04:33.170 So you could add a mechanism here with another variable that will keep the number of tries and continue 04:33.170 --> 04:37.310 to try again until you reach the maximum number of tries.