WEBVTT 00:00.080 --> 00:06.020 One of the most important things you want to do when programming is to avoid repeating code too much. 00:06.020 --> 00:08.060 So let's consider this program. 00:08.060 --> 00:09.530 Here I have first. 00:09.530 --> 00:12.380 So I declare a variable a is equal to two. 00:12.410 --> 00:14.330 And then I have three more variables. 00:14.330 --> 00:18.200 And for each one I actually want to do the triple of number a. 00:18.230 --> 00:19.400 So that's going to work. 00:19.400 --> 00:25.280 But instead of repeating the same code to triple the number, every time that we need to triple the 00:25.280 --> 00:29.720 number, let's create a function that does just that. 00:29.720 --> 00:31.100 So what is a function? 00:31.130 --> 00:36.590 A function is a reusable block of code that you can call from another part of your program. 00:36.620 --> 00:42.860 A function has a name, and it can take some input parameters and also can return some values if you 00:42.860 --> 00:43.310 want to. 00:43.340 --> 00:46.580 Let's create one function here so you will understand. 00:46.580 --> 00:49.670 And I'm going to do that at the beginning of the program here. 00:49.670 --> 00:53.270 So I'm just going to put a few more lines and let's create it there. 00:53.270 --> 00:58.220 So there is a specific syntax that you will use to create any function. 00:58.220 --> 01:01.520 The first thing to write is the keyword def. 01:01.550 --> 01:04.370 You can see we have a syntax highlighting for def. 01:04.400 --> 01:10.340 Okay so you write def and then space and you rewrite the name of the function. 01:10.340 --> 01:17.000 And best practice here is to use a meaningful name so that when somebody or you in the future read your 01:17.000 --> 01:18.800 function it makes sense. 01:18.830 --> 01:19.220 Okay. 01:19.250 --> 01:22.460 So we want to triple a number. 01:22.490 --> 01:26.900 Let's just call our function triple number. 01:26.930 --> 01:27.440 Okay. 01:27.470 --> 01:28.280 As simple as that. 01:28.280 --> 01:33.590 And as you can see if we want to have several words inside the function no problem. 01:33.590 --> 01:35.540 You just add an underscore okay. 01:35.570 --> 01:37.400 No space just an underscore. 01:37.430 --> 01:44.180 Then after the name of the function you will open and close parentheses and finish with a colon. 01:44.210 --> 01:47.990 Now in those parentheses you can add input parameters. 01:48.020 --> 01:48.200 Okay. 01:48.200 --> 01:52.700 So when we call the function we can send some data to the function. 01:52.700 --> 01:54.890 And the function can process this data. 01:54.890 --> 01:57.440 So for example numbers well any variable you want. 01:57.440 --> 02:00.860 And let's call this parameter here Number. 02:00.890 --> 02:01.100 Okay. 02:01.130 --> 02:04.940 So we create here a number as an input parameter. 02:04.970 --> 02:07.310 You can have zero parameter. 02:07.310 --> 02:08.390 You can have one parameter. 02:08.390 --> 02:10.670 You can have as many parameters as you want. 02:10.700 --> 02:13.850 You just separate them with a comma. 02:13.880 --> 02:14.210 Okay. 02:14.240 --> 02:16.550 So here for example I have three parameters. 02:16.880 --> 02:18.320 Let's just keep one. 02:18.320 --> 02:19.730 And then you will press. 02:19.730 --> 02:21.950 So after the colon here you press enter. 02:21.950 --> 02:26.540 And you can see that when we go back to a new line we don't go to the beginning of the line. 02:26.540 --> 02:27.560 We go to. 02:27.590 --> 02:31.280 You can see here we have four spaces. 02:31.280 --> 02:34.520 So we have an indentation of four spaces. 02:34.520 --> 02:36.710 And this indentation is very important. 02:36.710 --> 02:38.660 I'm going to come back to this a bit later. 02:38.660 --> 02:39.890 And here. 02:39.890 --> 02:46.430 So just after this line with this indentation we can start to write the code for the function. 02:46.430 --> 02:47.480 So you can write some code. 02:47.480 --> 02:51.050 And we can use the keyword return. 02:51.050 --> 02:55.250 So we return you finish the function and you return a value. 02:55.280 --> 02:56.630 What do we want to return. 02:56.630 --> 02:59.180 Well we have the number parameter here. 02:59.180 --> 03:01.250 We want to return number. 03:01.280 --> 03:03.260 Multiply by three. 03:03.290 --> 03:03.620 Okay. 03:03.650 --> 03:05.300 And that's it for the function. 03:05.300 --> 03:09.770 So we write def then the name of the function we open and close parentheses. 03:09.800 --> 03:12.080 We can add some input parameters. 03:12.080 --> 03:16.040 Then a colon we go back to a new line with an indentation. 03:16.040 --> 03:17.150 We can write some code. 03:17.150 --> 03:19.520 You can write code on several lines if you want to. 03:19.550 --> 03:21.500 And then you may return something. 03:21.500 --> 03:27.020 So if it's the case you just use the return keyword with some value here. 03:27.020 --> 03:30.770 And then after we have defined the function okay. 03:30.800 --> 03:34.010 So def is for define, then you can use it in the code. 03:34.010 --> 03:43.910 So instead of writing this here I can just do triple number and then pass a as an input parameter okay. 03:43.940 --> 03:49.340 So what will happen here is that I'm going to call this triple number function that's defined here. 03:49.340 --> 03:51.620 And at this point I'm going to pass a. 03:51.650 --> 03:55.220 So not a but actually the value inside a okay. 03:55.250 --> 04:02.780 So when I do this I'm going to call triple number with the value two okay is going to be received as 04:02.780 --> 04:04.550 the number parameter. 04:04.550 --> 04:07.460 So the number variable inside this function. 04:07.460 --> 04:09.680 And then it's going to return the number. 04:09.680 --> 04:12.890 So two times three is going to return six. 04:12.890 --> 04:14.660 So we have six as a result here. 04:14.660 --> 04:17.090 And let's just do the same. 04:17.090 --> 04:25.490 So let's just copy this one and put it there as well and there as well. 04:25.490 --> 04:31.550 And let's just because it's not going to print anything let's just print B for example okay. 04:31.580 --> 04:37.940 We print this variable here and you can see the result is six as I just explained. 04:37.940 --> 04:39.890 So that's how you create a function. 04:39.890 --> 04:41.390 And now you can do whatever you want here. 04:41.390 --> 04:52.280 For example we could say d is equal to triple number a and then plus triple number of c for example. 04:52.310 --> 04:54.170 Let's see what will happen. 04:54.170 --> 04:56.540 So I'm going to print D instead. 04:57.440 --> 05:00.500 And this time we have the value 24 Okay. 05:00.530 --> 05:00.770 Why? 05:00.800 --> 05:01.700 24. 05:01.730 --> 05:05.780 Because you can see we first call triple number A. 05:06.050 --> 05:06.260 Okay. 05:06.290 --> 05:09.200 So that will return six as we just saw previously. 05:09.200 --> 05:13.580 And then triple number C what's the value of C. 05:13.610 --> 05:18.320 Well the value of c is six because we have the triple of two. 05:18.350 --> 05:20.630 So the value of c is six. 05:20.720 --> 05:25.370 Here we pass six as a parameter to this function. 05:25.370 --> 05:28.520 And then it returns six times three. 05:28.550 --> 05:31.070 So it will return 18. 05:31.130 --> 05:31.310 Okay. 05:31.340 --> 05:33.350 So 18 plus six. 05:33.350 --> 05:34.400 We have 24. 05:34.430 --> 05:34.910 All right. 05:34.910 --> 05:38.600 And you have seen how to create a function that returns a value. 05:38.600 --> 05:40.220 But let's just create another function. 05:40.220 --> 05:41.900 So I'm going to I'm going to go back to a new line. 05:41.900 --> 05:46.520 You can see I go back to the previous indentation I go back to new line. 05:46.520 --> 05:48.800 Let's add some space for readability. 05:48.800 --> 05:53.120 And I'm going to create a new function that doesn't return anything. 05:53.120 --> 05:57.890 So I use def and let's say I want a function that prints the triple number. 05:57.890 --> 06:03.100 So let's just call it print Triple number. 06:04.540 --> 06:04.900 Okay. 06:04.930 --> 06:11.440 So instead of actually calling the function and then using print, we can do all of that with just one 06:11.440 --> 06:12.070 function. 06:12.070 --> 06:15.820 And I'm going to create an input parameter named number. 06:16.480 --> 06:19.870 I close the parentheses I add a colon. 06:19.870 --> 06:23.560 I go to a new line with enter okay new indentation. 06:23.560 --> 06:25.960 And how can I print the triple number. 06:25.990 --> 06:28.090 Well let's create a variable here. 06:28.090 --> 06:36.580 Result is equal to triple number and I will pass the number. 06:36.610 --> 06:37.060 Okay. 06:37.090 --> 06:41.980 So when I get to this print triple number function I receive a parameter called number. 06:41.980 --> 06:43.810 And I call the triple number function. 06:43.810 --> 06:46.120 So I call another function from this function. 06:46.180 --> 06:49.030 And I pass the value of number. 06:49.120 --> 06:49.360 Okay. 06:49.390 --> 06:53.290 This is going to go into this other number parameter. 06:53.290 --> 06:55.780 And it's going to return the number times three. 06:55.780 --> 06:57.400 So we get the result here. 06:57.400 --> 06:58.630 And then I can print. 06:58.630 --> 07:03.640 So you can see I can just press enter again and print the result. 07:03.670 --> 07:03.910 Okay. 07:03.940 --> 07:04.810 And we stay. 07:04.810 --> 07:08.200 You can see in the same indentation so that we are still in the function. 07:08.200 --> 07:10.840 So now I can call this function I'm just going to remove that. 07:10.840 --> 07:15.010 And let's say print triple number. 07:15.010 --> 07:18.790 And note here you can use Ctrl and space. 07:18.790 --> 07:20.290 And you will see this kind of stuff. 07:20.290 --> 07:21.820 And then you can press enter. 07:21.850 --> 07:25.300 Ctrl space is basically the Autocompletion tool okay. 07:25.330 --> 07:27.880 In programming you will see you will use that a lot. 07:27.910 --> 07:29.080 Autocompletion. 07:29.080 --> 07:36.430 You can start a variable name, a function name for example, and then press Ctrl Space Anthony and 07:36.430 --> 07:41.320 you will get suggestions about how to finish your variable or your function. 07:41.320 --> 07:46.420 And as you progress with programming, you will use that a lot, because what it will make you gain 07:46.420 --> 07:52.360 a lot of time and also you will make less errors because the name for sure will be correct. 07:52.390 --> 07:56.200 Okay, you don't have any risk of making a typo if you use Autocompletion. 07:56.230 --> 07:56.560 All right. 07:56.560 --> 08:00.910 So I'm going to do print triple number and let's give five. 08:01.000 --> 08:01.450 Okay. 08:01.480 --> 08:02.620 Just like that. 08:02.620 --> 08:04.990 So to call a function, you can see that. 08:05.020 --> 08:06.370 Yeah we have to call. 08:06.370 --> 08:09.040 So we have to write the name of the function. 08:09.040 --> 08:14.980 And then open and close parentheses and provide the required amount of parameters. 08:14.980 --> 08:16.060 We just have one. 08:16.060 --> 08:21.850 But if you had several parameters you would need to add a comma between each parameter. 08:22.330 --> 08:23.590 Let's run that. 08:23.590 --> 08:25.510 And you can see we have 15. 08:25.570 --> 08:28.000 So in this case we go. 08:28.000 --> 08:29.560 So we call print number. 08:29.560 --> 08:32.080 We go here five goes here. 08:32.260 --> 08:36.070 Then five goes to triple number function okay. 08:36.100 --> 08:37.180 Multiply by three. 08:37.210 --> 08:39.790 We return it inside the result variable. 08:39.790 --> 08:42.340 And then we print the result variable okay. 08:42.370 --> 08:45.220 You can see the flow of execution here. 08:45.220 --> 08:49.060 And one thing I can improve here is well I just create a variable and I print it. 08:49.060 --> 08:52.210 But I don't really use that that much. 08:52.210 --> 08:55.510 So I can just instead do print. 08:56.470 --> 08:59.890 I open the parentheses and I close the parentheses here. 09:00.010 --> 09:02.620 And I'm going to remove this line. 09:03.490 --> 09:10.750 So you can see here I use a function okay inside a function. 09:10.750 --> 09:15.340 So the result of triple number is going to be used for the print function. 09:15.700 --> 09:15.910 All right. 09:15.940 --> 09:18.370 So you can combine functions like this. 09:18.370 --> 09:23.500 And let's finish with a third function I'm just going to call it say hello. 09:23.530 --> 09:25.240 This function just says hello. 09:25.240 --> 09:28.090 And I'm not going to pass any parameter okay. 09:28.090 --> 09:31.870 So you can see def then say hello open close parentheses colon. 09:31.870 --> 09:35.560 Go to a new line print just hello. 09:35.680 --> 09:36.160 All right. 09:36.160 --> 09:39.880 And that's a very simple and basic function I can call it here. 09:39.910 --> 09:47.200 Say hello okay I need to open and close parentheses always to call the function. 09:47.200 --> 09:50.680 Let's run this and you can see we have hello. 09:50.710 --> 09:50.920 Okay. 09:50.950 --> 09:54.190 So that's another example of a function that doesn't return anything. 09:54.190 --> 09:57.970 And it also doesn't get any input parameters. 09:57.970 --> 10:02.230 So to recap a function is a reusable block of code. 10:02.230 --> 10:07.960 It has a name, it can have some input parameters, and it can also return something. 10:07.960 --> 10:09.520 And there's a lot of flexibility. 10:09.550 --> 10:12.460 You can call a function within another function. 10:12.460 --> 10:15.520 You can combine functions together, etc.. 10:15.550 --> 10:15.910 Okay. 10:15.940 --> 10:16.780 And a function. 10:16.780 --> 10:21.040 As you can see, a function that you define does nothing on its own okay. 10:21.070 --> 10:24.640 It's kind of a template that you can use to be able to use the function. 10:24.640 --> 10:27.820 You actually need to call the function as we did here. 10:27.820 --> 10:30.640 And finally you should always right. 10:30.640 --> 10:32.890 So you should define the function before you use it. 10:32.920 --> 10:33.280 Okay. 10:33.310 --> 10:38.050 If I try to run this line before I define the function, it's not going to work. 10:38.050 --> 10:41.770 So you always have to define the function first and then use it. 10:41.800 --> 10:45.100 If you don't do that, you will simply get an undefined error. 10:45.130 --> 10:45.310 Okay. 10:45.340 --> 10:50.650 That says that for example the triple number is undefined and then you know that you need to define 10:50.650 --> 10:52.510 it before you use it. 10:52.540 --> 10:52.930 All right. 10:52.960 --> 10:55.720 And we will come back very often to functions in this course. 10:55.720 --> 10:57.460 We will use them everywhere. 10:57.460 --> 11:00.400 So they will be more opportunities for you to practice.