WEBVTT 00:00.080 --> 00:00.440 Great. 00:00.440 --> 00:05.090 You can now create basic Python programs using variables and functions. 00:05.090 --> 00:12.410 But before we go any further, there is one thing you need to clearly understand and this is the scope 00:12.410 --> 00:16.070 of a variable or also called the visibility of a variable. 00:16.070 --> 00:23.390 So depending on where you create a variable, it may or may not be accessible from other parts of the 00:23.390 --> 00:24.140 program. 00:24.140 --> 00:28.250 And let's understand that with an example I'm just going to keep this file here. 00:28.250 --> 00:29.810 And I'm going to add a few lines. 00:29.810 --> 00:31.700 We're going to come back to this in a minute. 00:31.760 --> 00:33.680 But for now let's write some new code here. 00:33.680 --> 00:39.200 So I will define a new variable I will call it e for example is equal to three. 00:39.200 --> 00:41.900 And I will define a function here. 00:41.900 --> 00:44.360 Let's say print e okay. 00:44.390 --> 00:45.740 Very dumb function. 00:45.770 --> 00:52.640 Kind of useless but just for the purpose of this video and print e for example I use. 00:52.640 --> 00:56.810 So basically I use the variable inside a function okay. 00:56.870 --> 01:02.510 And let's call that here um print e okay. 01:02.510 --> 01:04.670 Let's run that. 01:04.940 --> 01:06.350 You can see we have three. 01:06.350 --> 01:11.640 So we have the rest of the of the file here that's Also being executed. 01:11.640 --> 01:12.960 But we have three here. 01:12.960 --> 01:13.710 Print e. 01:13.980 --> 01:14.250 Okay. 01:14.280 --> 01:15.540 So we create a variable here. 01:15.540 --> 01:16.920 We use it in the function. 01:16.950 --> 01:19.650 Now I'm going to create another function. 01:19.680 --> 01:22.470 Or actually I can just use this function. 01:22.470 --> 01:26.220 And let's say I'm creating a new variable named test okay. 01:26.250 --> 01:28.200 That value is ten. 01:28.200 --> 01:32.520 And now let's say I want to print test okay. 01:32.550 --> 01:36.570 So I create this variable inside this function. 01:36.570 --> 01:39.930 And after that I try to print this variable. 01:39.930 --> 01:41.670 So let's see what you can guess. 01:41.670 --> 01:43.170 What would be the result of that. 01:43.170 --> 01:45.180 Will we see ten. 01:46.620 --> 01:49.740 And as you can see we actually have an error okay. 01:49.770 --> 01:54.300 So the first three is printed because we could print the value. 01:54.300 --> 01:59.580 But then when we try to print test you see test is not defined. 01:59.580 --> 02:00.390 Why is that. 02:00.390 --> 02:03.750 We just created test here and we can't use it here. 02:03.750 --> 02:06.720 Well that is because of the scope. 02:06.720 --> 02:13.020 So when you create a variable at the top of your program here or anywhere without any indentation, 02:13.020 --> 02:14.880 you can use it everywhere. 02:14.880 --> 02:18.720 After that, it is what we call a global variable. 02:18.750 --> 02:22.960 But when you create a variable inside a block of code with an indentation. 02:22.960 --> 02:25.090 So for example here inside a function. 02:25.090 --> 02:32.950 So when you create a variable inside a block of code with indentation, this variable is a local variable 02:32.950 --> 02:35.050 for this indentation. 02:35.080 --> 02:35.230 Okay. 02:35.260 --> 02:37.000 So we call this a local variable. 02:37.000 --> 02:42.220 And so this test variable is created inside this function. 02:42.220 --> 02:47.020 And we cannot use it outside of this indented block of code. 02:47.020 --> 02:51.370 And after the block of code is executed here the variable is basically gone. 02:51.400 --> 02:57.640 The only way to get access to that variable is between its creation here and the end of the block of 02:57.640 --> 03:01.390 code, and the rule with scope is quite simple. 03:01.420 --> 03:09.790 A variable will be visible in the scope it's created in, and in every nested scope inside this initial 03:09.790 --> 03:10.360 scope. 03:10.360 --> 03:16.030 For example, this variable we created here will be available well everywhere here and inside this function 03:16.030 --> 03:18.430 because this is a nested scope okay. 03:18.460 --> 03:20.110 Which means that we have an indentation. 03:20.110 --> 03:21.220 It's a nested scope. 03:21.220 --> 03:28.060 But the variable we create here is not available here simply because while this one is a more global 03:28.060 --> 03:29.580 scope than this one. 03:29.580 --> 03:34.260 So to go from here to there, we basically have to go back one indentation. 03:34.290 --> 03:34.440 Okay. 03:34.470 --> 03:39.180 If you go back one indentation, basically you lose the visibility of that variable. 03:39.180 --> 03:42.180 And for now we only have one level of indentation. 03:42.180 --> 03:45.870 But then as we progress you will see that we can have many more levels. 03:45.900 --> 03:46.080 Okay. 03:46.110 --> 03:48.720 Which means that we have more nested scopes. 03:48.720 --> 03:51.930 And I want to show you something else that's linked to the scope. 03:51.930 --> 03:55.470 And that's actually quite practical here for us actually. 03:55.470 --> 04:01.680 So you can see we have those two, those two functions here triple number and print triple number. 04:01.680 --> 04:06.240 And both of them have a number input parameter. 04:06.240 --> 04:09.360 So what happens actually when you have an input parameter. 04:09.360 --> 04:14.310 Well this is going to create a local variable inside the function. 04:14.340 --> 04:21.060 And you can see actually when I click here this and that one is the same when I click here this one 04:21.060 --> 04:23.040 and that one are the same variable. 04:23.040 --> 04:26.430 So we create a local variable inside the function. 04:26.430 --> 04:33.540 And as you know with the scope this here number variable is only going to be available in that function. 04:33.540 --> 04:37.320 And this one is only going to be available in that function here. 04:37.320 --> 04:42.010 So that's why we can have several functions with several input parameters. 04:42.010 --> 04:48.220 And those parameters can actually have the same name, but they actually represent completely different 04:48.220 --> 04:49.480 variables okay. 04:49.510 --> 04:52.870 Because to go from this function to that function it's simple. 04:52.870 --> 04:53.890 You are here. 04:53.890 --> 04:55.960 So you need to go back one indentation. 04:56.380 --> 04:57.370 Then you lose the well. 04:57.370 --> 05:02.140 You lose the visibility because you need to go back one indentation and then go to that one and the 05:02.140 --> 05:03.820 same on the opposite way. 05:03.820 --> 05:10.030 To go from this function to that function, you first need to go out of the scope and then back in another 05:10.030 --> 05:10.690 scope. 05:10.690 --> 05:13.360 So then we lose the visibility. 05:13.360 --> 05:19.420 So once again any parameter that you create in a function is basically going to create a local variable 05:19.420 --> 05:23.140 inside that function that is only accessible in this function. 05:23.140 --> 05:27.850 And also any nested scope that you create in that function. 05:27.850 --> 05:33.820 So as a conclusion to this lesson, when working with variables, always keep in mind the scope of the 05:33.820 --> 05:34.690 variables. 05:34.720 --> 05:41.290 Is this variable declared in a more general or a more local scope, and in the scope that I am currently 05:41.290 --> 05:44.110 writing in, can I get access to a variable? 05:44.110 --> 05:48.520 And when you get used to it, it's very simple to spot the scope of any variable.