WEBVTT 0 00:00.290 --> 00:04.040 To get started, we're going to learn more about functions. 1 00:04.040 --> 00:13.040 And previously, we learned that functions are a really handy way of taking a complex set of instructions 2 00:13.040 --> 00:19.760 and packaging them together inside a block of code that has a name given to it. 3 00:19.760 --> 00:26.720 And when we need all of the lines of code that's packaged inside this function, all we have to do at 4 00:26.720 --> 00:34.160 any point later on in our code is just to call the function by typing its name, and then a set of parentheses. 5 00:34.490 --> 00:40.850 And when this line of code is run, it's going to search for where this function is defined, which is 6 00:40.850 --> 00:41.540 up here. 7 00:41.540 --> 00:45.770 And then it's going to execute all the lines of code that are contained within it. 8 00:46.490 --> 00:49.280 Now it's been a little while since we've seen functions. 9 00:49.280 --> 00:53.880 So to begin I want you to create a new function called greet(), 10 00:53.880 --> 00:59.430 and I want you to give it three lines of print() statements telling it to do three things. 11 00:59.430 --> 01:05.820 And finally, once you're done, go ahead and call the function so that it gets executed in the console. 12 01:05.820 --> 01:08.040 So pause the video and give that a go. 13 01:09.150 --> 01:09.660 All right. 14 01:09.660 --> 01:13.050 So to create a function we of course need the 'def' keyword, 15 01:13.050 --> 01:17.340 and we know it's a keyword because as soon as we type it it changes the color. 16 01:17.430 --> 01:21.720 And after the keyword, we get to give our function a name. 17 01:21.720 --> 01:24.090 So in my case it's called greet. 18 01:24.210 --> 01:29.610 Now after the greet, we add a set of parentheses after the name of the function. 19 01:29.940 --> 01:36.990 Finally, we add a colon and we enter into the block of code because we're indented over. 20 01:37.260 --> 01:42.270 Now, the first thing I'm going to do is to create a print statement that just says, "Hello". 21 01:42.270 --> 01:46.110 And then I'm going to say, well, "How do you do?" 22 01:46.230 --> 01:52.980 Now, nobody in England actually says this, but I always see it in the Learn English books, which 23 01:52.980 --> 01:53.880 is quite funny. 24 01:53.880 --> 01:55.770 I think people will give you very strange looks, 25 01:55.770 --> 01:58.650 if you go to somebody at the bakery and say, well, "How do you do?" 26 01:59.610 --> 02:08.320 But anyways, now finally we're going to add a final print statement, keeping in line with the Britishness 27 02:08.320 --> 02:12.670 of my function, I'm going to ask about the weather. 28 02:13.480 --> 02:19.480 Now, this line, on the other hand, is something that you will often hear British people say, they're 29 02:19.480 --> 02:23.620 obsessed about the weather, mostly because it's terrible all the time. 30 02:23.620 --> 02:29.410 So now that we've created our function, it's time to actually trigger the function or what we say in 31 02:29.410 --> 02:35.680 programming lingo, call the function, and we do that by calling the name of the function and then 32 02:35.680 --> 02:37.300 adding a set of parentheses. 33 02:37.300 --> 02:43.270 And now once the code reaches Line 6, it's going to search for this greet() function, which it'll find 34 02:43.270 --> 02:44.140 over here. 35 02:44.140 --> 02:48.070 And then it's going to carry out each of the lines of code one by one. 36 02:48.070 --> 02:53.350 So let's run the code and you should see each of the three print statements being called. 37 02:53.350 --> 02:55.120 So that's pretty simple. 38 02:55.810 --> 03:02.830 Notice that every single time I call the greet() function, it's going to do the same thing, right? 39 03:02.830 --> 03:05.800 It's just going to print out those three lines of code. 40 03:05.830 --> 03:12.730 Now in reality, it's very rare that you'll want to repeat the same instructions every single time 41 03:12.730 --> 03:14.080 when you call a function, 42 03:14.080 --> 03:20.590 it would be nice, wouldn't it? If we could modify some of the parts of the code inside the function 43 03:20.590 --> 03:23.650 and allow for a little bit of variation. 44 03:23.650 --> 03:30.070 For example, it'd be nice if we could greet somebody by their name so they could say, "Hello Angela," instead 45 03:30.070 --> 03:37.210 of just "Hello." "How do you do Angela?" So that it could change each time I call this function? 46 03:37.210 --> 03:41.620 Maybe next time it'll be, "How do you do Jack Bauer?" Et cetera. 47 03:41.620 --> 03:45.340 So how can we achieve this kind of functionality? 48 03:45.340 --> 03:49.540 Well, we need to look more closely at these parentheses. 49 03:49.570 --> 03:58.480 Now what we can do is we can actually add the name of a variable inside those parentheses to start giving 50 03:58.480 --> 04:00.370 our functions some inputs. 51 04:00.370 --> 04:06.140 So let's say that there's a variable called 'something' that's going to be passed to my_function. 52 04:06.140 --> 04:13.310 And this something can then be used inside this block of code, this function. 53 04:13.310 --> 04:15.320 And I could do something with it. 54 04:15.320 --> 04:22.340 Now in order to actually pass this value, when I call my_function, I have to add the data inside the 55 04:22.340 --> 04:23.120 parentheses. 56 04:23.120 --> 04:27.020 So let's say I decide to pass 123 over. 57 04:27.020 --> 04:33.380 Well, in this case, when this line of code gets triggered, the computer is going to search for where 58 04:33.380 --> 04:35.720 this function is declared, which is up here, 59 04:35.720 --> 04:44.000 and then it's going to pass over this piece of data 123, over to this variable called something. 60 04:44.000 --> 04:51.320 So now effectively inside this function called my_function, we now have a variable called something 61 04:51.320 --> 04:58.880 that's equal to 123, and that can then be used inside the block of code to do something with 62 04:58.880 --> 05:00.020 that piece of data. 63 05:01.100 --> 05:05.390 Now it's a bit like plugging a USB stick into a computer. 64 05:05.570 --> 05:12.500 If we took a different piece of input, we would end up with a different file being shown by the computer. 65 05:12.530 --> 05:18.980 So this means the computer can do something different depending on the input that we give it. 66 05:18.980 --> 05:23.390 And if we change that input, then it will receive a different piece of data. 67 05:23.960 --> 05:30.260 So in addition to a simple function, we can also create a function that allows for input. 68 05:30.740 --> 05:36.140 And to do that you saw earlier on the syntax is again the same as before, 69 05:36.140 --> 05:42.840 we use a 'def' to create the function and then let's just give it a slightly different name to differentiate 70 05:42.840 --> 05:48.900 it with the previous function greet_with_name() and then inside the parentheses, 71 05:48.900 --> 05:54.630 instead of leaving it blank, we get to create the name of the variable that's going to be passed over. 72 05:54.630 --> 05:59.820 So let's just call it 'name' because that describes the data that's going to be received. 73 05:59.820 --> 06:02.940 It's going to be the name of the person that I wish to greet. 74 06:02.940 --> 06:05.160 So now let's add a colon. 75 06:05.160 --> 06:08.280 And finally we can create our print statements. 76 06:08.490 --> 06:11.520 So I'm just going to copy these print statements from above. 77 06:11.520 --> 06:17.430 And now, instead of having these names hard-coded in here, I'm going to delete it, 78 06:17.430 --> 06:22.800 and I'm going to replace those names with the value of this variable. 79 06:22.800 --> 06:27.210 So I'm going to put it in using an f-string, like this. 80 06:27.210 --> 06:30.340 And then I'm going to do the same down here. 81 06:34.600 --> 06:39.670 When we actually call this function, it's also going to be a little bit different from previously on 82 06:39.670 --> 06:40.570 Line 6. 83 06:40.570 --> 06:44.260 So now, firstly the name of the function has changed. 84 06:44.260 --> 06:49.930 But notice how it's expecting some sort of input inside the parentheses, 85 06:49.930 --> 06:52.780 and it tells me that it wants to receive a name. 86 06:52.900 --> 06:58.810 It's when we call the function that we actually pass over the piece of data that's going to be stored 87 06:58.810 --> 07:00.880 inside this variable. 88 07:00.880 --> 07:03.520 Let's give it my own name, "Angela". 89 07:03.520 --> 07:09.550 And now when I hit Run, I want you to predict what's going to happen, what's actually going to be 90 07:09.550 --> 07:10.180 printed. 91 07:10.180 --> 07:14.110 So let's go ahead and comment out the previous line of code, 92 07:14.200 --> 07:16.660 and now run our code. 93 07:16.750 --> 07:19.850 And you should see that it says, "Hello Angela". 94 07:19.850 --> 07:20.930 "How do you do Angela?" 95 07:20.930 --> 07:25.610 So this piece of data has basically been inserted under this variable name, 96 07:25.610 --> 07:29.120 and then it's been put into both of these print statements. 97 07:29.120 --> 07:36.860 Now if I go ahead and call this function with a different piece of data, say a different name, then 98 07:36.860 --> 07:41.030 it's going to use that piece of data to modify this function 99 07:41.030 --> 07:43.750 so it does something a little bit different. 100 07:43.750 --> 07:49.000 So this way we can create one function that carries out some instructions, 101 07:49.000 --> 07:55.450 but every time we execute it, we get to modify it a little bit by changing the input. 102 07:56.170 --> 08:01.540 When we're talking about functions with inputs, there's two things that we're working with that's really 103 08:01.540 --> 08:03.370 important to differentiate. 104 08:03.850 --> 08:11.230 So we know that when we call this function and we pass over this piece of data, effectively we're creating 105 08:11.230 --> 08:13.660 a new variable called, something, 106 08:13.660 --> 08:17.770 and we're setting it to equal this piece of data that we're passing in. 107 08:17.980 --> 08:25.270 Now in programming lingo, you'll hear this being referred to as the Parameter, and this piece of data 108 08:25.270 --> 08:28.030 being referred to as the Argument. 109 08:28.600 --> 08:35.230 Now the argument is the actual piece of data that's going to be passed over to this function when it's 110 08:35.230 --> 08:39.970 being called, whereas the parameter is the name of that data, 111 08:39.970 --> 08:45.460 and we use the parameter inside the function to refer to it and to do things with it. 112 08:45.670 --> 08:51.280 Now, very often on the internet, when you come across somebody explaining something, be it on StackOverflow 113 08:51.280 --> 08:57.420 or in some piece of documentation, you'll hear them referring to these two types of things the parameter 114 08:57.420 --> 08:58.680 and the argument. 115 08:58.710 --> 09:04.230 So if you need to come back to this lesson and remind yourself the difference between those two things, 116 09:04.230 --> 09:07.590 the parameter is the name of the data that's being passed in, 117 09:07.590 --> 09:10.950 the argument is the actual value of the data. 118 09:11.310 --> 09:16.740 Now, sometimes people also get confused on the internet between these two words, but as long as you 119 09:16.740 --> 09:19.080 know what they mean, then you'll be in a good place.