WEBVTT 00:00.110 --> 00:04.400 In this lesson you will learn how to work with Python inside the terminal. 00:04.430 --> 00:07.430 We will start our Python programs directly from the terminal. 00:07.430 --> 00:09.500 We will also improve them. 00:09.500 --> 00:11.480 So let's start actually with the Python shell. 00:11.480 --> 00:14.690 This is something that we have seen at the very beginning of the course. 00:14.690 --> 00:20.990 So if I come back to thonny, while the shell is what you have on the bottom right, and if you remember 00:20.990 --> 00:23.690 we did something like print hello. 00:25.070 --> 00:25.220 Okay. 00:25.220 --> 00:27.980 You can run commands right here from the shell. 00:28.010 --> 00:32.960 And so this is something you can do in Thonny, but you can also do that directly from the terminal. 00:32.990 --> 00:36.500 How to do this you just type Python three. 00:36.530 --> 00:39.830 You press enter and you are in a Python shell. 00:39.830 --> 00:41.330 So I can do print. 00:42.350 --> 00:44.510 Hello for example. 00:44.510 --> 00:46.040 Well, I can do whatever I want. 00:46.070 --> 00:51.710 I can create a variable, I can print this variable. 00:51.710 --> 00:54.710 I can just run any Python comment that I want. 00:54.740 --> 00:59.930 And note here that if I press Ctrl C, you see I have a keyboard interrupt. 00:59.930 --> 01:01.880 We can come back to this at the end of this video. 01:01.880 --> 01:05.530 So we have a keyboard interrupt, but we are still in the shell. 01:05.560 --> 01:07.030 How to exit from the shell. 01:07.030 --> 01:13.840 We have the exit function with parentheses and then we are back to the terminal. 01:13.870 --> 01:14.170 All right. 01:14.200 --> 01:17.560 So if you want to use the shell you can see you just type Python three. 01:17.590 --> 01:21.910 Then you just know that you have to also write exit with parentheses to exit. 01:21.910 --> 01:23.890 And you can use the Python shell as you want. 01:23.920 --> 01:28.000 Now you can also run a Python program directly from the terminal. 01:28.000 --> 01:29.530 That's going to be super useful. 01:29.530 --> 01:30.070 Let's go. 01:30.070 --> 01:36.760 So with CD to documents and Python programs LZ what do we have here. 01:36.760 --> 01:39.460 So for example we have the Hello.py. 01:39.490 --> 01:43.690 So what we have done so far is for example we go on file, we open. 01:44.740 --> 01:46.180 Uh let's go back to this. 01:46.180 --> 01:46.690 Hello. 01:46.720 --> 01:49.000 Well you can just open any program okay. 01:49.000 --> 01:50.020 It doesn't matter here. 01:50.020 --> 01:52.420 You see that we can click on run. 01:52.420 --> 01:53.710 That's what we've done here. 01:53.740 --> 01:58.420 And so here well it's going to create a variable and then print the same variable three times. 01:58.420 --> 02:00.730 So we have 12 1212 as a result. 02:00.730 --> 02:04.200 So let's go back to the terminal and how to run this in the terminal. 02:04.200 --> 02:07.440 Well, you just use Python three, just like we did before. 02:07.440 --> 02:12.090 But then instead of just running Python three, you do space and you provide the file name. 02:12.090 --> 02:15.960 And this file name must be a Python file with the Python extension. 02:15.990 --> 02:16.410 Okay. 02:16.410 --> 02:18.120 So for example hello. 02:18.120 --> 02:21.120 And I can press tab for autocompletion okay. 02:21.150 --> 02:22.410 Hello.py. 02:22.410 --> 02:25.470 And you see we execute this from the terminal okay. 02:25.500 --> 02:27.390 So that's going to be very useful. 02:28.320 --> 02:32.460 And before we go further just a quick parenthesis if you run. 02:32.460 --> 02:38.940 So sometimes might happen if you run a program that uses the Gpio library. 02:38.940 --> 02:43.200 So for example if you use the push button, the LED, the Pi R sensor etc.. 02:43.200 --> 02:48.660 So if you use a program that uses the Gpio zero library here and then you try to. 02:48.690 --> 02:52.530 So if you run this on Sony and then you try to run it on the terminal, maybe you're going to get an 02:52.530 --> 02:54.420 error in the terminal. 02:54.420 --> 02:59.640 And if that happens, well what you have to do is to close first Tony okay. 02:59.670 --> 03:04.410 So you close Tony completely and then you run the code on the terminal. 03:04.440 --> 03:09.970 So just in case you have an issue with the Gpio zero, when you actually run it from one side and the 03:09.970 --> 03:10.480 other side. 03:10.480 --> 03:15.730 But as we will see later in this course, every time that we want to run a program with Gpio, it's 03:15.730 --> 03:17.920 going to be better to do it from the terminal. 03:17.920 --> 03:23.140 So now that you can use the Python shell and execute programs from the terminal, let's create a new 03:23.140 --> 03:25.960 file, let's edit it and let's run it. 03:25.960 --> 03:28.720 And so for example you can create a new file from Thonny. 03:28.720 --> 03:30.550 But you could also create it from the terminal. 03:30.550 --> 03:37.780 So I can do here I'm in my Python program I can do touch test dot pi for example. 03:37.780 --> 03:41.560 And then I could edit it with Nano or with any other program. 03:41.560 --> 03:43.690 But here, for example I can go back to Tony. 03:46.390 --> 03:52.750 And I can do file open and I can find this paste test dot pi. 03:52.780 --> 03:53.170 All right. 03:53.170 --> 03:56.710 So this way we actually don't create the file from Tony but from the terminal. 03:56.740 --> 03:57.970 Then where to edit the file. 03:57.970 --> 04:01.930 Well if you're going to create a Python program with at least a few lines. 04:01.960 --> 04:07.210 Actually Tony is better for this because you have the syntax highlighting, you have the Autocompletion. 04:07.240 --> 04:11.980 The interface is quite easy to use, so you can definitely write your code here. 04:11.980 --> 04:16.840 And then if you want to run it well for quick test, you can definitely run it from Thonny, but you 04:16.840 --> 04:18.790 can also run it directly from the terminal. 04:18.790 --> 04:21.550 So you could write the code here and run it from the terminal. 04:21.580 --> 04:26.560 For example, if you want to run the code later and you don't want to open Thonny when the code is already 04:26.560 --> 04:28.450 written, you can just do this from the terminal. 04:28.480 --> 04:34.150 Or if, let's say you don't have access to the desktop, if you don't have access to VNC or a screen, 04:34.150 --> 04:41.020 and if you only have an SSH access, then from SSH you can go on the terminal and you can execute this 04:41.020 --> 04:43.060 script with the command python3. 04:43.090 --> 04:48.430 Also, if you want to automate your Python program and run it from another program, well you will need 04:48.430 --> 04:50.890 to use the command from the terminal. 04:50.920 --> 04:51.490 All right. 04:51.490 --> 04:56.500 And now to finish this, I'm going to show you a way that you can improve your code. 04:56.500 --> 04:58.780 And this is something also related to the terminal. 04:58.780 --> 05:01.270 So let's write a simple code here. 05:01.270 --> 05:05.590 Print begin okay. 05:05.620 --> 05:10.850 And then print And so nothing special is going to print. 05:11.090 --> 05:13.910 Well, begin in a line and then end in another line. 05:14.000 --> 05:16.850 Now let's say I have a while loop. 05:17.000 --> 05:26.810 Let's say while true and I do print a and well let's not print A too fast. 05:26.810 --> 05:37.040 So I'm going to do import time and then I will do so here time.sleep. 05:37.250 --> 05:40.790 Let's say we print a every 0.5 seconds. 05:40.820 --> 05:41.090 All right. 05:41.120 --> 05:43.280 So you can see if I run it from here. 05:43.970 --> 05:46.910 Well you see begin a a a and then I stop. 05:46.940 --> 05:47.720 That's it. 05:47.750 --> 05:48.710 We don't see the end. 05:48.740 --> 05:50.750 That's kind of what you expected, right? 05:50.780 --> 05:52.790 I can also run it from the terminal. 05:52.820 --> 05:59.600 So Python three test.py begin a a a and then how to stop it? 05:59.630 --> 06:01.760 Well we're going to press control C. 06:01.880 --> 06:02.180 Okay. 06:02.210 --> 06:06.170 So if you want to stop a running script from the terminal you press control C. 06:06.170 --> 06:11.810 And here you can see we have a keyboard Interrupts and the program just ends like this. 06:11.840 --> 06:14.060 Of course, we don't execute the end. 06:14.090 --> 06:15.890 Actually, we could also. 06:15.890 --> 06:23.090 So if I run the script from Tony, we can also click here and press control C you see directly from 06:23.090 --> 06:23.390 the shell. 06:23.390 --> 06:27.380 So you have to click on the shell and then press Ctrl C and you see we have the keyboard interrupt. 06:27.380 --> 06:29.420 So that's something you can also do on Tony. 06:29.450 --> 06:31.100 Now this can be fine. 06:31.100 --> 06:37.970 But if you want to end your scripts in a bit more clean way, or if you want, for example, to be able 06:37.970 --> 06:44.390 to execute the last line or a few more instructions after you decide to exit from the script, then 06:44.390 --> 06:45.110 how can you do that? 06:45.140 --> 06:48.830 Well, you can use a try catch block. 06:48.830 --> 06:50.120 So let me write this. 06:50.120 --> 06:56.180 You will use try like this but a colon and then everything that you want to run here. 06:56.180 --> 07:02.390 For example this while loop you put it in the try like that with an indentation okay. 07:02.420 --> 07:05.360 So you see now this is indented inside the try. 07:05.360 --> 07:07.550 And then you go back to a new line. 07:07.550 --> 07:13.650 You come back here and you write accept because you accept because actually we're going to catch an 07:13.680 --> 07:14.640 exception. 07:14.640 --> 07:17.280 And what is the exception we want to catch? 07:17.280 --> 07:19.740 This is a keyboard interrupt. 07:19.770 --> 07:24.570 So you're going to write keyboard like that interrupt. 07:24.570 --> 07:28.410 And as you see try and accept a recognized keyword. 07:28.440 --> 07:31.680 We also have syntax highlighting for keyboard interrupt. 07:32.100 --> 07:33.450 You put a colon here. 07:33.450 --> 07:39.810 You go back to new line and let's say print uh quotes exception. 07:41.100 --> 07:42.750 So what this is going to do. 07:42.750 --> 07:45.900 Well the try is just going to run this normally. 07:45.900 --> 07:51.570 But then if you press Ctrl C because this is going to be a keyboard interrupt, instead of exiting from 07:51.570 --> 07:57.390 the program you will kind of catch the exception here, catch the control C and then be able to print 07:57.390 --> 07:59.580 that and then finish the program. 07:59.580 --> 08:04.950 I'm going to save with Ctrl s and well let's run it from the terminal again. 08:05.670 --> 08:09.270 Now I press Ctrl C and you see what we have the control C here. 08:09.270 --> 08:11.400 But you see we have code exception. 08:11.400 --> 08:14.010 That's the log here and then end. 08:14.040 --> 08:17.520 So we don't finish the script with an error. 08:17.550 --> 08:17.970 Okay. 08:18.000 --> 08:20.670 And we can also execute the last line of the program. 08:20.670 --> 08:22.140 And one more thing here. 08:22.140 --> 08:24.510 Well, we could decide to do nothing. 08:24.540 --> 08:30.960 Actually, when we catch this exception, we could decide to do nothing and just print n. 08:30.960 --> 08:33.540 But if we run that, we're going to get an error. 08:33.600 --> 08:39.690 Okay, that's the indentation error because, well, you cannot have a block of code that contains nothing. 08:39.690 --> 08:41.580 So what if you want to actually do nothing. 08:41.580 --> 08:42.660 Well you have a keyword. 08:42.660 --> 08:43.770 It's called pass. 08:43.770 --> 08:48.990 So this way you say, well pass is just I don't want to execute anything, but because I have to write 08:48.990 --> 08:51.900 something then I just write pass, I'm going to save. 08:51.960 --> 08:58.590 And now it's going to work so I can run the program again from what Tony or the terminal and control 08:58.620 --> 09:02.550 C you see we have end and this way it's a bit more clean. 09:02.580 --> 09:02.970 All right. 09:02.970 --> 09:08.160 So in this lesson you have seen how to work with Python from the terminal and also how to improve your 09:08.160 --> 09:14.610 programs so that when you press control C on the terminal you can actually catch this keyboard interrupt.