WEBVTT 00:00.080 --> 00:06.380 This is the solution for the activity number seven, where we start from the code of the activity, 00:06.410 --> 00:10.400 six, where we switch the LED when we press on the push button. 00:10.400 --> 00:14.120 And we improve this with lists. 00:14.120 --> 00:21.560 So the goal is to make that code work for any amount of LEDs and to have a code that's as clean as possible. 00:21.560 --> 00:22.970 And let's get started. 00:22.970 --> 00:28.130 So I have written this for you to know that we have the Len function. 00:28.130 --> 00:30.950 To know the length of a list, I'm going to remove that. 00:31.400 --> 00:38.930 And what I have already done is to create this LED list here with LED one, two and three. 00:38.930 --> 00:40.280 So what can we do? 00:40.310 --> 00:43.400 First you see that we turn off all LEDs. 00:43.400 --> 00:49.070 So that's going to be a small first exercise to practice a bit with lists and loops. 00:49.070 --> 00:51.680 If we want to turn off all the LEDs here. 00:51.680 --> 00:56.360 So we want to do something on each element of the list we can use. 00:56.360 --> 00:58.040 So I'm going to remove this. 00:58.490 --> 01:04.380 Those lines here we can use a for loop and we're going to iterate over each element. 01:04.410 --> 01:05.430 So for. 01:05.460 --> 01:09.990 I will need to put a local variable that I'm going to use for each element. 01:10.020 --> 01:11.070 Let's call it LED. 01:11.490 --> 01:14.550 For LED in LED list. 01:14.580 --> 01:15.150 Okay. 01:15.150 --> 01:21.180 So for element in list I put a colon I go to a new line. 01:21.180 --> 01:22.680 And then when I do LED. 01:23.250 --> 01:26.970 This LED corresponds to well each element. 01:26.970 --> 01:29.970 So the for loop is going to be run here three times. 01:30.000 --> 01:35.670 The first time we're going to get LED one and then led two and then led three. 01:35.670 --> 01:38.730 So I can just do LED dot off. 01:38.940 --> 01:39.570 Okay. 01:39.600 --> 01:41.940 That's going to turn the LED off. 01:41.940 --> 01:44.340 So the first one the second one and the third one. 01:44.340 --> 01:47.520 So with this we can already initialize all LEDs. 01:47.520 --> 01:54.240 And you can see that if we have one, two, 7 or 20 LEDs the code is going to be the same. 01:54.240 --> 01:58.470 Then what I told you we keep this LED index at the end. 01:58.500 --> 01:59.890 We keep those two lines. 01:59.890 --> 02:05.470 So now the challenge is what do we do with this switch LED. 02:05.860 --> 02:12.730 I'm going to keep this global lead index because we're going to still need to use and modify the LED 02:12.730 --> 02:13.840 index variable. 02:13.870 --> 02:19.720 But then I'm going to write the new code here and I will just comment on those lines. 02:19.780 --> 02:21.430 So we will remove those. 02:21.430 --> 02:25.330 But I will first comment those lines. 02:25.330 --> 02:26.650 So comment. 02:29.350 --> 02:34.210 Just so we can keep them for now to see what was the previous code. 02:34.210 --> 02:37.000 And then when we are done I'm just going to remove everything. 02:37.000 --> 02:45.370 So in the end let's look at what we did here and what kind of global behavior we can implement. 02:45.370 --> 02:47.800 That's going to be valid for any amount of LEDs. 02:47.800 --> 02:56.500 So every time what you can see is that we turn off all the LEDs and we turn on only the LED that corresponds 02:56.500 --> 02:57.640 to the index. 02:57.670 --> 02:58.000 All right. 02:58.030 --> 03:00.860 So actually one we reset all the LEDs. 03:00.860 --> 03:04.400 Two we set the LED that corresponds to the index. 03:04.400 --> 03:05.690 So we turn on that LED. 03:05.690 --> 03:09.590 And then three we do LED index plus one. 03:09.590 --> 03:12.830 So that the next time it's going to be for the next LED. 03:13.010 --> 03:13.280 All right. 03:13.310 --> 03:16.190 So that's how we can see what we have to do. 03:16.220 --> 03:17.660 We have three steps here. 03:17.660 --> 03:19.520 First we turn off all the LEDs. 03:19.520 --> 03:22.880 Then we turn on only the LED that corresponds to the index. 03:22.880 --> 03:25.460 And then we increment that index. 03:25.460 --> 03:30.080 And now the thing is maybe you implemented something a bit different. 03:30.110 --> 03:30.530 Okay. 03:30.560 --> 03:32.840 There is not only one solution okay. 03:32.870 --> 03:35.270 This solution I'm showing you is my solution. 03:35.270 --> 03:37.550 And well, it's a pretty efficient one. 03:37.550 --> 03:43.460 But maybe you've come up with something else that works and that is as valid as my solution. 03:43.460 --> 03:45.440 So let me implement that. 03:45.440 --> 03:49.100 What I will do is I will just say that we turn off all LEDs. 03:49.100 --> 03:57.050 So for LED in LED list we do LED dot off. 03:57.810 --> 03:59.850 That's the that's the same thing we did here. 03:59.880 --> 04:00.480 Okay. 04:00.660 --> 04:07.020 And then I will do what I will do because we have a list and we have an index. 04:07.020 --> 04:11.820 And we can get access directly to an element of a list with the index. 04:11.820 --> 04:21.030 So if I do LED list and I put those brackets and I do LED index the first time, it's going to be zero. 04:21.030 --> 04:25.950 So you can see if I do LED list zero I get the first LED. 04:26.070 --> 04:33.750 If the index is one then I will get LED list with one, I will get the second element etc. so I can 04:33.750 --> 04:36.120 just do LED list with the index. 04:36.120 --> 04:39.330 I will get the LED and then I do dot on. 04:39.870 --> 04:40.320 All right. 04:40.320 --> 04:45.120 We turn off all LEDs and we turn on only one LED. 04:45.210 --> 04:51.090 You might think that's a bit redundant because here let's say we want to turn on the first LED. 04:51.120 --> 04:54.000 We're going to turn it off first and then turn it on. 04:54.000 --> 04:57.350 So yes, there is an extra step that's going to be done. 04:57.350 --> 05:00.050 But first it's going to happen very fast. 05:00.050 --> 05:02.900 So it's not going to slow down the program or anything. 05:02.900 --> 05:06.380 And it's going to make our program and our life much easier to do this. 05:06.410 --> 05:06.890 All right. 05:06.890 --> 05:12.320 So let's see what's going to happen for now when we press on the pause button this is going to be called 05:12.320 --> 05:14.210 we turn off all the LEDs. 05:14.210 --> 05:18.470 And then we're going to turn on the first one with index zero. 05:18.470 --> 05:19.760 So that's going to be led one. 05:19.790 --> 05:20.450 Great. 05:20.480 --> 05:23.840 And then the next time we press on the push button same thing. 05:23.840 --> 05:28.160 So now we need to make sure that we can go to the next LED. 05:28.190 --> 05:29.090 How to do this. 05:29.090 --> 05:33.590 Well we do LED index plus equals one. 05:33.590 --> 05:37.130 So we add one to the LED index so that the next time. 05:37.130 --> 05:39.050 So the LED index will be one. 05:39.050 --> 05:43.880 When we call the switch LED again we're going to turn off all LEDs. 05:43.880 --> 05:49.940 And then we turn on the one with the index one which is actually the second LED. 05:49.940 --> 05:51.740 And then we're going to do plus one. 05:51.740 --> 05:53.930 So the index is going to be two. 05:53.960 --> 06:00.620 Which means that the third time we call the switch LED function, we're going to turn on the third LED. 06:00.680 --> 06:00.950 All right. 06:00.980 --> 06:02.210 But then you can see there's a problem. 06:02.210 --> 06:07.670 If I just leave the code like this, then we're going to get a out of range. 06:07.670 --> 06:14.990 Because next time the LED index will be three which is zero, one, two and three which doesn't exist. 06:14.990 --> 06:16.340 So we're going to get an error. 06:16.340 --> 06:21.590 So we need to go back at the beginning of the list when we have reached the end. 06:21.620 --> 06:23.450 Now what is the end of the list. 06:23.480 --> 06:33.230 We're not just going to write a if LED index is equal to three. 06:33.260 --> 06:39.020 Because what we want to make it dynamic so that it works for any amount of LEDs. 06:39.050 --> 06:39.260 Okay. 06:39.290 --> 06:48.320 So instead of hard coding a value we will just check if the LED index is greater or equal than the length 06:48.320 --> 06:49.880 of the list. 06:49.880 --> 06:53.540 So that's why we use the Len function here. 06:55.020 --> 06:57.600 So what is the length of the list here? 06:57.600 --> 07:04.350 The length is three, but if your array or your list contains seven elements, then the length is going 07:04.350 --> 07:08.280 to be seven so that you can count until seven. 07:08.280 --> 07:12.270 So we check if the LED index is equal to or greater. 07:12.300 --> 07:15.180 Actually just equal would work. 07:15.480 --> 07:19.140 But just to be safe we can put greater or equal. 07:19.140 --> 07:20.670 Then the length of the list. 07:20.700 --> 07:27.090 We know we have reached the end, so we just need to do LED index is equal to zero okay. 07:27.120 --> 07:29.460 This is a very common thing to do in Python. 07:29.550 --> 07:32.670 You increment by one and you check when you reach the end. 07:32.670 --> 07:34.980 When you reach the end, you go back to the beginning. 07:35.010 --> 07:35.520 All right. 07:35.520 --> 07:39.570 And with this we should be able to run the code. 07:39.570 --> 07:42.210 So I can remove this. 07:42.210 --> 07:46.680 You can see that now the code is even smaller than this. 07:46.740 --> 07:47.940 So I'm going to remove that. 07:47.970 --> 07:53.670 The code is smaller but it can also work for any amount of LEDs. 07:53.670 --> 07:55.730 So let's run. 07:56.690 --> 07:57.410 All right. 07:57.440 --> 07:57.860 All right. 07:57.890 --> 07:59.000 Activity seven. 07:59.150 --> 08:02.150 And you can see all LEDs are turned off. 08:02.150 --> 08:03.770 Now I press on the push button. 08:03.770 --> 08:07.460 We have the first one, then the second one, then the third one. 08:07.460 --> 08:09.800 And then we should go back to the first one. 08:09.830 --> 08:10.430 All right. 08:10.430 --> 08:12.500 And you can see it correctly works. 08:12.500 --> 08:18.140 And just to show you that it can work with any amount of LEDs, let's say that instead of three LEDs 08:18.140 --> 08:19.370 I only have two. 08:19.550 --> 08:25.580 So I'm going to I'm going to just close the bracket here, and I'm going to use a comment here just 08:25.580 --> 08:27.020 to comment the end of the line. 08:27.020 --> 08:31.610 So you can see now our list only contains two LEDs. 08:31.820 --> 08:33.500 Let's run this code instead. 08:34.790 --> 08:35.330 Okay. 08:35.360 --> 08:37.160 All LEDs are turned off. 08:37.160 --> 08:38.360 I press on the push button. 08:38.360 --> 08:42.290 We have the first one I press again, I have the second one. 08:42.290 --> 08:43.160 And now look. 08:43.160 --> 08:47.090 If I press again we go back to the first LED okay. 08:47.120 --> 08:50.870 So we are just going between the two LEDs and the third one. 08:50.870 --> 08:54.360 No, because the third one is not in the list. 08:55.170 --> 08:55.500 All right. 08:55.500 --> 08:58.590 So you can see the problem is much more dynamic now. 08:58.800 --> 09:00.900 So I will do a quick recap of what we did. 09:00.900 --> 09:04.830 And then there are still a few improvements in the code that we can do. 09:04.830 --> 09:07.170 So let's recap first. 09:07.200 --> 09:10.680 All right so we start with the LED index at zero. 09:10.710 --> 09:15.090 We register this function that's going to be called whenever we press on the push button. 09:15.090 --> 09:23.190 So the first time the index is zero we turn off all LEDs and we turn on the first LED which corresponds 09:23.190 --> 09:25.320 to the first index. 09:25.320 --> 09:27.300 Then we do plus one. 09:27.300 --> 09:34.230 We check actually if the LED index, which is not equal to one, is greater or equal than the length 09:34.230 --> 09:35.160 of the list. 09:35.160 --> 09:37.740 So with this example, the length of the list is two. 09:37.770 --> 09:40.230 So is one greater or equal than two. 09:40.260 --> 09:41.250 This is false. 09:41.250 --> 09:43.200 So we don't execute that line okay. 09:43.230 --> 09:46.590 Now the next time we switch the button we go back here. 09:46.620 --> 09:49.350 Now the LED index is one. 09:49.350 --> 09:51.360 So we turn off all LEDs. 09:51.360 --> 09:56.200 We turn on the LED with the index one, which is here, the LED number two. 09:56.230 --> 09:57.430 And then we do plus one. 09:57.430 --> 09:59.710 So the index is now equal to two. 09:59.740 --> 10:04.540 And with this configuration with two LEDs well the length is going to be two. 10:04.570 --> 10:07.450 So is two greater or equal than two. 10:07.480 --> 10:07.900 Yes. 10:07.900 --> 10:11.020 So we go back to index zero okay. 10:11.050 --> 10:14.290 And we go back then to the first LED here. 10:14.320 --> 10:14.650 All right. 10:14.680 --> 10:17.860 So you can see it works with any number of LEDs. 10:17.890 --> 10:27.460 Because then if I remove this comment and that bracket now when we reach LED index two the length is 10:27.460 --> 10:28.150 three. 10:28.180 --> 10:30.670 So we're going to go one more time. 10:30.700 --> 10:31.000 All right. 10:31.030 --> 10:35.560 If you have six LEDs you're going to go from 012345. 10:35.560 --> 10:37.630 When you reach six you go back to zero. 10:37.660 --> 10:38.140 Great. 10:38.140 --> 10:42.670 And now just a few things to optimize the code a bit more. 10:42.670 --> 10:46.480 So first of all, so I told you you could do this. 10:46.480 --> 10:50.920 You just add you create the LEDs and then you add them in the list. 10:50.920 --> 10:52.550 But here LED one. 10:52.550 --> 10:55.820 We only use it to actually put it inside the list. 10:55.850 --> 11:02.990 We don't use it anywhere else directly, so instead of creating a variable and putting it in the list, 11:03.020 --> 11:05.870 we can just create it in the list. 11:05.870 --> 11:08.330 So I can do LED here. 11:08.360 --> 11:09.440 17. 11:10.340 --> 11:10.670 All right. 11:10.700 --> 11:15.110 That's going to create an LED variable and put it inside the LED list. 11:15.170 --> 11:23.930 Same thing for LED two I can do LED with 27. 11:25.130 --> 11:28.790 And then I can do LED with 22. 11:29.510 --> 11:30.020 All right. 11:30.020 --> 11:30.920 And that's it. 11:30.920 --> 11:34.430 And I can remove those three lines. 11:34.910 --> 11:37.370 So now let's say you have added another LED. 11:37.820 --> 11:40.160 So you put LED like this. 11:40.160 --> 11:45.680 You put the Gpio number and you don't need to modify anything else in the code. 11:47.240 --> 11:47.480 All right. 11:47.480 --> 11:48.500 So I'm going to remove that. 11:48.500 --> 11:57.420 And the thing we can improve here is also that you see we run this for loop here and also here. 11:57.420 --> 11:59.130 What do we do with this for loop? 11:59.130 --> 12:02.340 Basically we turn off all LEDs. 12:02.340 --> 12:05.670 We could also say that we reset the LEDs. 12:05.700 --> 12:11.490 Okay, so instead of writing the code twice we could create a function. 12:11.580 --> 12:19.920 So what I could do is I could create a function def reset LEDs like that. 12:20.130 --> 12:22.560 No input parameters, no need. 12:22.560 --> 12:25.890 And inside I will just put those lines. 12:29.220 --> 12:35.190 So instead of repeating this block of code, every time that we need to run that we can just call reset 12:35.220 --> 12:36.000 LEDs. 12:36.030 --> 12:36.420 Okay. 12:36.450 --> 12:39.150 And because I've created a function now I should actually call it. 12:39.150 --> 12:41.730 So I should do reset LEDs. 12:42.930 --> 12:48.660 And just to make things a bit, uh, well, a bit cleaner because here we create a function. 12:48.660 --> 12:51.670 Then we call the function and then we define another function. 12:51.670 --> 12:59.470 So instead of putting reset LEDs here I'm going to go down and I'm going to put it there. 12:59.740 --> 13:00.520 Okay. 13:00.520 --> 13:06.220 So what we do is we first initialize some stuff. 13:06.220 --> 13:09.400 So maybe I can even put the variable here. 13:09.400 --> 13:11.260 You can see I can move stuff around. 13:11.260 --> 13:16.870 As long as I define everything before I use it I can move stuff around. 13:17.560 --> 13:17.830 All right. 13:17.830 --> 13:19.750 And with this it's better we create. 13:19.750 --> 13:21.220 So we have our input. 13:21.220 --> 13:23.590 Then we create our global variables. 13:23.590 --> 13:30.490 Then we have our functions, and then we have our code which is just reset LEDs and then register this 13:30.490 --> 13:32.440 function and then pause. 13:32.470 --> 13:33.190 All right. 13:33.190 --> 13:37.810 And what I have created this function here so I can use it here as well. 13:37.810 --> 13:44.500 So I'm going to remove this block of code and just say reset LEDs like that. 13:44.500 --> 13:48.760 And don't forget to put the parentheses here because we call the function great. 13:48.760 --> 13:52.950 And you can see now the code is dynamic and optimized. 13:52.980 --> 13:53.250 Okay. 13:53.280 --> 13:55.560 So the code is 22 lines of code. 13:55.560 --> 13:59.490 It's not a lot but it's doing quite a lot already. 13:59.490 --> 14:02.760 Let's just check that it works so you can just run. 14:02.790 --> 14:04.860 I'm just going to press just to check. 14:04.860 --> 14:07.560 And what I see that it works. 14:07.560 --> 14:09.540 So all good okay. 14:09.570 --> 14:11.100 Don't forget to test your program. 14:11.100 --> 14:14.250 If you improve them even if you didn't add a new functionality. 14:14.280 --> 14:14.700 Great. 14:14.700 --> 14:16.350 So that's the end of this activity. 14:16.380 --> 14:21.810 It was a bit more complex than what we've done previously, but that was to show you that with just 14:21.810 --> 14:26.340 a few lines of Python code, you can do a lot of things with Gpios. 14:26.340 --> 14:31.500 Now don't worry if you found those two last activities quite difficult. 14:31.530 --> 14:36.090 Okay, we're going to continue with more hardware components and with more concepts in the Raspberry 14:36.090 --> 14:36.480 Pi. 14:36.510 --> 14:39.660 So you may want to do those activities again in a few days. 14:39.660 --> 14:45.210 But in the meantime, I encourage you to also continue with the course to discover the next few concepts 14:45.210 --> 14:49.560 which will allow you to do really nice projects with your Raspberry Pi.