WEBVTT 00:00.080 --> 00:06.290 This is the solution for the activity for where you have to get the user input, and depending on that 00:06.290 --> 00:10.760 user input, you're going to turn off or turn on the LED. 00:10.760 --> 00:13.490 And we're going to make sure that the user gives us 0 or 1. 00:13.490 --> 00:17.120 If it's any other value, we're going to print an error message. 00:17.120 --> 00:21.230 So let's get started I'm first going to remove this because this is not code. 00:21.260 --> 00:24.230 It was just some instructions that I gave you. 00:24.230 --> 00:26.390 And well I already have this. 00:26.390 --> 00:29.300 So I have a variable called user choice. 00:29.300 --> 00:30.650 And I get the input. 00:30.650 --> 00:35.150 I cast this as an integer and I can have a prompt. 00:35.150 --> 00:36.860 So let's not leave this empty. 00:36.890 --> 00:39.800 Let's try to prompt that makes sense okay. 00:39.830 --> 00:42.410 And that gives the user enough information. 00:42.410 --> 00:43.970 So we get the correct value. 00:43.970 --> 00:59.870 So I can say for example enter zero to turn off the LED and then one to turn it on with a column and 00:59.870 --> 01:00.620 a space. 01:00.620 --> 01:02.480 So we have our user input. 01:02.510 --> 01:07.190 Now, before we go any further, let's actually initialize our LED. 01:07.370 --> 01:10.280 So I'm going to put that a bit lower. 01:10.280 --> 01:12.380 And I'm going to start with the inputs. 01:12.380 --> 01:17.150 So as best practice just put all the inputs at the beginning of your program. 01:17.150 --> 01:20.120 So we will need from Gpio zero. 01:20.150 --> 01:23.330 We will need the so import LED. 01:23.420 --> 01:30.620 And then because we also want to wait some time in the program, I'm just going to do import time so 01:30.620 --> 01:32.210 that we can do Time.sleep. 01:32.240 --> 01:32.630 Great. 01:32.630 --> 01:34.280 So that's all for the import. 01:34.310 --> 01:36.230 Now we can initialize the LED. 01:36.320 --> 01:39.200 So once again let's keep things simple. 01:39.200 --> 01:43.310 Let's create an LED variable is equal to LED uppercase. 01:43.310 --> 01:48.860 And then in the parentheses we specify the Gpio which is still 17. 01:48.890 --> 01:50.330 Okay we haven't changed the circuit. 01:50.330 --> 01:52.040 So now the LED is initialized. 01:52.040 --> 01:56.240 And we're going to ask the user input. 01:56.270 --> 01:57.770 So I just put this here. 01:57.800 --> 01:58.190 Okay. 01:58.220 --> 02:00.410 You can see I just add some spaces. 02:00.440 --> 02:02.900 It's just for the readability of the program. 02:02.930 --> 02:03.140 Okay. 02:03.170 --> 02:06.770 You could add zero spaces, but then it's going to be a bit hard to read. 02:06.800 --> 02:07.190 Great. 02:07.190 --> 02:09.740 And what do I do with this user choice. 02:09.770 --> 02:11.870 Well here I'm going to use an if. 02:11.960 --> 02:17.780 And I'm going to do if user choice is equal to zero. 02:17.780 --> 02:20.960 And so pay attention here is not just one equal sign. 02:20.960 --> 02:23.060 It's two equal sign. 02:23.090 --> 02:23.330 Okay. 02:23.360 --> 02:30.440 So once again one equal sign is used to assign a value from the right to the left. 02:30.440 --> 02:33.710 But two equal sign is going to compare two values. 02:33.740 --> 02:37.730 So for example with zero and then a colon. 02:37.730 --> 02:43.400 So it's going to compare those two values and return true or false. 02:43.430 --> 02:43.610 Okay. 02:43.640 --> 02:47.450 So true if they are equal and false if they are not equal. 02:47.450 --> 02:52.490 So if the user choice is equal with two equal to zero what do we want to do. 02:52.520 --> 03:00.620 Well we want to turn off the LED so we can do LED, sort of as simple as that. 03:00.620 --> 03:04.250 Then I go back to a new line and that's it for this block of code. 03:04.250 --> 03:05.600 We don't want to do anything else. 03:05.600 --> 03:11.630 So I'm going to go back to the previous indentation and add an L if okay. 03:11.660 --> 03:14.390 So if the user choice this time is equal. 03:14.390 --> 03:18.800 So user choice is equal with double equal to one. 03:18.830 --> 03:20.810 Then I put a colon. 03:20.810 --> 03:25.340 We go back to a new line with an indentation LED dot on. 03:26.000 --> 03:27.710 So I turn on the LED. 03:27.740 --> 03:29.660 So you might think well that's it. 03:29.660 --> 03:31.910 But we also want to validate the input. 03:31.910 --> 03:38.720 Which means that if the value is not correct we want to also say, well the choice is an invalid choice. 03:38.720 --> 03:41.060 It must be 0 or 1. 03:41.060 --> 03:45.080 So I'm going to go back to a new line again previous indentation. 03:45.080 --> 03:47.000 And I can just put else. 03:47.000 --> 03:54.500 So whatever value that is not 0 or 1 is going to fall under the else else I go back to a new line with 03:54.500 --> 03:57.770 an indentation and I can put for example, print. 03:58.430 --> 04:04.610 Invalid choice must be 0 or 1. 04:04.640 --> 04:08.960 You can also decide to print the choice if you want. 04:08.990 --> 04:15.050 In this case, make sure that you cast this as a string, because here it's an integer. 04:15.050 --> 04:16.250 So we print that. 04:16.250 --> 04:19.130 And then I'm also going to add exit here. 04:19.130 --> 04:22.070 And I will tell you why in just one minute. 04:22.070 --> 04:27.950 Because what we want to do next is that after we turn off or we turn on the LED, we just want to wait 04:27.950 --> 04:29.450 for two seconds. 04:29.450 --> 04:38.120 So what I could do is to do time dot sleep with two and then time to sleep with two here, etc. but 04:38.150 --> 04:45.920 I'm just going to put the time.sleep after this if like this time.sleep with two. 04:46.250 --> 04:52.310 Which means that if we turn off or if we turn on, the LED is going to wait for two seconds anyway, 04:52.310 --> 04:55.430 so we just need to write Time.sleep only once. 04:55.430 --> 05:03.050 And in this case I have added the exit keyword here because if the choice is invalid, we don't want 05:03.050 --> 05:04.280 to wait for two seconds. 05:04.280 --> 05:07.850 So in this case we just exit from this point. 05:07.880 --> 05:11.780 Okay, so to recap we first do all the imports that we need. 05:11.810 --> 05:13.250 We initialize the LED. 05:13.250 --> 05:16.400 We get the user input that we cast as an int. 05:16.400 --> 05:20.060 And then we check if it's zero we power it off. 05:20.060 --> 05:21.170 So we power off the LED. 05:21.290 --> 05:23.840 If it's one we power on the LED. 05:23.930 --> 05:29.090 And also so after this, after either this instruction or that instruction, we're going to go out of 05:29.090 --> 05:31.490 the if and wait for two seconds. 05:31.490 --> 05:36.470 But still in the if if the user choice is not 0 or 1, we print an error message. 05:36.470 --> 05:40.010 So error message is basically just a normal message. 05:40.010 --> 05:42.920 And then we also exit from the program. 05:42.920 --> 05:45.470 So we don't execute that line of code. 05:45.470 --> 05:49.490 And maybe I can just print end here. 05:49.490 --> 05:53.090 So it's going to be even easier to see when the program ends. 05:53.120 --> 05:53.570 All right. 05:53.570 --> 05:55.790 So let's start this. 05:55.790 --> 06:01.610 And as you can see when you initialize the LED it's going to be turned off by default. 06:01.610 --> 06:06.590 And we have enter 0 or 1 here I'm just going to go with one. 06:06.590 --> 06:08.480 For example I press enter. 06:08.480 --> 06:13.070 You see the LED is turned on and after two seconds we have end. 06:13.190 --> 06:14.360 We can start again. 06:15.170 --> 06:17.450 And then I will say zero. 06:17.780 --> 06:20.810 So actually the LED is already powered off. 06:20.990 --> 06:24.920 But if I do zero well you see the LED is still powered off. 06:24.920 --> 06:26.240 And then we have end. 06:26.240 --> 06:29.360 And let's test the last case. 06:29.390 --> 06:31.310 Let's say I give a wrong value. 06:31.310 --> 06:36.830 So three in this case you see invalid choice must be 0 or 1. 06:36.830 --> 06:39.590 And actually here you see we still have the end. 06:39.620 --> 06:43.130 We still have the time.sleep because it's my mistake. 06:43.130 --> 06:44.450 I gave you the exit keyword. 06:44.450 --> 06:46.490 It's actually the exit function. 06:46.520 --> 06:46.700 Okay. 06:46.700 --> 06:48.800 You can see it can be very different. 06:48.830 --> 06:53.930 He exit is a real keyword, but it's not going to do the same thing as the function. 06:53.960 --> 06:56.600 So the function is going to actually exit from the program. 06:56.600 --> 06:59.570 And to call the function you have to use parentheses. 06:59.600 --> 06:59.750 Okay. 06:59.750 --> 07:00.830 Let's try again. 07:01.250 --> 07:02.960 I'm going to give three again. 07:04.340 --> 07:04.640 Okay. 07:04.670 --> 07:06.380 And you can see we have. 07:06.410 --> 07:09.080 So we even have another message here. 07:09.080 --> 07:12.080 Process ended with exit code zero. 07:12.080 --> 07:16.400 And this time we didn't wait for two seconds and we don't print the end. 07:16.430 --> 07:16.760 All right. 07:16.790 --> 07:22.040 And I'm going to leave this mistake here in the video just to show you that as you can see, sometimes 07:22.070 --> 07:23.600 things will work. 07:23.600 --> 07:28.670 So you're not going to get an error when you run the code, but it's not going to work as you want because 07:28.670 --> 07:33.710 maybe you forgot some parentheses, or maybe you added extra parentheses that you shouldn't have. 07:33.740 --> 07:39.230 Or you can see there can be a lot of different things like that that will give you a behavior that you 07:39.230 --> 07:39.980 don't want. 07:40.010 --> 07:42.560 So pay attention to everything you type, okay. 07:42.560 --> 07:45.200 And double check your code before you run it. 07:45.230 --> 07:45.710 All right. 07:45.710 --> 07:47.540 And that's the end of this activity.