WEBVTT 0 00:06.140 --> 00:13.850 Coming back to our original example, I want to talk more about the Global Scope, and the concept of 1 00:13.850 --> 00:16.940 modifying something within the global scope. 2 00:17.360 --> 00:22.520 Here we have enemies, which is a variable that has global scope, 3 00:22.610 --> 00:27.860 and here we have a function which creates a local scope. 4 00:28.040 --> 00:33.930 Now we think that we're tapping into this variable and setting it to 2, 5 00:34.020 --> 00:40.590 but in fact, we're actually creating a completely new variable that's entirely separate from this one. 6 00:41.040 --> 00:46.530 And this is why when we printed it here, it showed it was equal to 2, 7 00:46.530 --> 00:51.150 but when we printed it here, it showed it was actually equal to 1. 8 00:51.390 --> 00:55.760 If you want to make this a little bit more obvious, I can call this a "Skeleton", 9 00:55.760 --> 00:59.210 and I can set this to be a "Zombie". 10 01:00.200 --> 01:04.910 And when I hit Run, you can see again, this prints 'Zombie', 11 01:04.910 --> 01:06.740 this prints 'Skeleton'. 12 01:06.740 --> 01:11.930 Because these two variables are actually entirely different things. 13 01:11.930 --> 01:15.890 And we're not changing this right here at all, 14 01:15.890 --> 01:19.790 we're just creating a new variable that has a local scope. 15 01:20.760 --> 01:29.130 Now, it's usually a terrible idea to call your local variables and your global variables the same name. 16 01:29.130 --> 01:36.270 But in this case, what we actually wanted to do was we wanted to modify this variable. 17 01:36.270 --> 01:39.810 We wanted to do something like maybe + = 1. 18 01:39.810 --> 01:46.430 And notice how as soon as I write + = 1, then my editor starts going crazy and tells me that 19 01:46.430 --> 01:53.750 this local variable 'enemies' is defined in an enclosing scope is referenced before assignment. 20 01:53.750 --> 01:54.590 What does that mean? 21 01:54.590 --> 02:00.890 It means that the editor thinks you're trying to tap into a local variable that you defined somewhere 22 02:00.890 --> 02:08.570 around here, and then you try to modify it by adding one to the previous value, but you actually haven't 23 02:08.570 --> 02:09.470 defined it. 24 02:10.100 --> 02:17.070 What we wanted to do, though, is we wanted to tap into this variable and change it here. 25 02:18.000 --> 02:26.130 In order to do this, we actually have to explicitly say that we have a global variable which is called 26 02:26.130 --> 02:33.120 enemies, that's defined somewhere outside of this function, and that is the enemies that we want to 27 02:33.120 --> 02:35.130 use inside this function. 28 02:35.130 --> 02:41.740 So it basically takes that global enemies into the function and allows you to modify it. 29 02:41.740 --> 02:49.090 Without this line of code, we cannot modify something that is global within a local scope. 30 02:50.680 --> 02:56.770 Now, there's a reason why it's so difficult to modify something that has global scope. 31 02:56.770 --> 03:04.860 You probably don't actually want to do this very often because it's confusing and it's prone to creating 32 03:04.860 --> 03:12.240 bugs and errors, because this variable with global scope could have been created anywhere in your code, 33 03:12.240 --> 03:12.690 right? 34 03:12.690 --> 03:18.150 And you would be modifying it completely independent of when you created it. 35 03:18.150 --> 03:23.400 So it might have been days between when you wrote this code and when you wrote this code, 36 03:23.400 --> 03:28.040 and it just makes everything more fallible, more easy to fail. 37 03:28.040 --> 03:35.750 This is why very often people will tell you when they're teaching you Python to avoid modifying global 38 03:35.750 --> 03:36.410 scope. 39 03:36.410 --> 03:37.730 You can read it, 40 03:37.730 --> 03:38.780 that's not a problem, 41 03:38.780 --> 03:47.900 you can use it within your code like we are here but don't try to modify it within a function that 42 03:47.900 --> 03:49.070 has local scope. 43 03:49.070 --> 03:50.690 But what can you do instead? 44 03:50.690 --> 03:56.610 What if you wanted to have this functionality like a function that changes the number of enemies? 45 03:56.640 --> 04:01.770 How can you achieve this without modifying the global scope within the function? 46 04:01.920 --> 04:07.620 Well, you could use what we learned about return statements instead, right? 47 04:07.740 --> 04:15.420 What if instead of modifying the enemies, you actually just simply returned it as the output? 48 04:15.420 --> 04:19.540 So return the current value of enemies + 1. 49 04:19.780 --> 04:26.020 Now, once you call this function, you'll get hold of the outputs and you can save it to the global 50 04:26.020 --> 04:27.460 variable enemies. 51 04:27.460 --> 04:33.550 So this now means that this function can be taken away and placed anywhere in your code, and you don't 52 04:33.550 --> 04:39.940 actually need to know how it works, as long as you know that this is how you increase enemies, then 53 04:39.940 --> 04:42.370 all you have to do is just call it.