WEBVTT 0 00:00.140 --> 00:01.040 To begin, 1 00:01.040 --> 00:05.600 the first thing I want to talk about is more on functions. 2 00:05.600 --> 00:09.290 So we've already seen a couple of things that we can do with functions. 3 00:09.320 --> 00:15.860 The first thing I showed you was how to create a very simple bog-standard function using the def, the 4 00:15.860 --> 00:22.310 name, the empty parentheses, and then the colon, and then within the body of the function, you can 5 00:22.310 --> 00:30.200 do a bunch of things which will be carried out every single time you trigger, or call the function like 6 00:30.200 --> 00:30.830 this. 7 00:30.860 --> 00:36.500 And the first type of function basically just helps you reduce the amount of code you have to write 8 00:36.500 --> 00:39.950 when you have instructions that you want to execute repeatedly. 9 00:40.460 --> 00:45.590 Now the next type of function we saw actually had something inside the parentheses. 10 00:45.590 --> 00:52.190 And this something is an input which can be passed over when we call the function. 11 00:52.220 --> 00:59.420 So in this case 123 is the argument which gets passed in to this parameter called something, 12 00:59.420 --> 01:02.760 and then it gets used within the body of the function. 13 01:02.790 --> 01:06.630 The second type of function, the functions which allow for inputs, 14 01:06.660 --> 01:13.260 gives us the ability to modify the code in the function, and to get it to do something different each 15 01:13.260 --> 01:16.710 time, depending on what input was passed in. 16 01:16.740 --> 01:20.910 We're now onto the final sort of flavor of functions, 17 01:20.910 --> 01:28.500 and these are functions which allow you to have an output once the function is completed. 18 01:28.530 --> 01:31.500 We start off with a simple function, 19 01:31.500 --> 01:36.930 and in this case, you'll notice that even though I could, I'm actually not giving it any inputs, the 20 01:36.930 --> 01:40.080 inputs and the outputs are completely separate from each other. 21 01:40.080 --> 01:43.680 So this is a normal function that you've seen many times now. 22 01:43.680 --> 01:49.230 And within the body of the function I'm going to do some piece of calculation. 23 01:49.230 --> 01:55.050 Let's say I'm going to calculate what is 3 * 2, and then save it to a variable called result. 24 01:55.080 --> 02:03.570 Now once that's done I can use the output keyword, which is return, and then after that keyword I 25 02:03.570 --> 02:08.340 can put whatever it is I want to be the output of this function. 26 02:08.340 --> 02:11.730 So in this case the output is the result. 27 02:11.730 --> 02:21.270 And what that means is when I call this function later on and it runs, then it will go ahead and output 28 02:21.270 --> 02:22.530 this result, 29 02:22.530 --> 02:27.930 and it replaces this line of code where this function was called. 30 02:27.960 --> 02:32.760 Now that result is held in the code where the function was called, 31 02:32.760 --> 02:36.360 and I could save it to another variable. 32 02:36.390 --> 02:39.330 Result of course equals, 3 * 2, 33 02:39.330 --> 02:42.990 and that means this output now equals 6. 34 02:42.990 --> 02:45.360 So this is what the code might look like. 35 02:45.360 --> 02:52.440 Somewhere I would define my function which has an output which you can tell by the 'return' keyword. 36 02:52.470 --> 02:59.710 Now at some other point in my code, I decide to call that function, and once that function executes, 37 02:59.710 --> 03:07.360 that return or whatever is outputted replaces the function call, and at the very end, it means this 38 03:07.360 --> 03:11.260 variable output will store whatever the output is. 39 03:11.260 --> 03:14.920 So in this case, output would be equal to six. 40 03:15.400 --> 03:21.100 The way that I like to think about functions with outputs is almost kind of like a machine, right? 41 03:21.130 --> 03:28.840 If you had a machine where in goes some empty bottles and after some processing or some inputs, out 42 03:28.840 --> 03:31.480 comes a bottle filled with milk. 43 03:31.480 --> 03:36.550 So in this case this function has an input the empty glass bottle, 44 03:36.550 --> 03:40.240 it has an output, the glass bottle filled with milk, 45 03:40.270 --> 03:47.050 and in the middle there's some processes or some code that's being executed to create this change. 46 03:47.230 --> 03:50.920 This ties together all the things that we've learned about functions. 47 03:50.920 --> 03:54.520 So now head over to the starting file for today's lessons. 48 03:54.520 --> 04:00.920 Let's start off by creating a new function, which I'm going to call format_name. 49 04:00.920 --> 04:09.290 And the reason is because this function is going to take a first name and a last name, and it's going 50 04:09.290 --> 04:16.580 to change those inputs, even if it was lowercase or if it was all caps, it's going to change it into 51 04:16.610 --> 04:23.210 title case, something like this, where the first letter is capitalized in each word. 52 04:23.900 --> 04:30.890 To begin, I want you to create this function and then go ahead and add two inputs to it, one called 53 04:30.920 --> 04:31.640 f_name, 54 04:31.640 --> 04:37.010 so first name, and another called l_name, which is the last name. 55 04:37.040 --> 04:38.840 Pause the video and give that a go. 56 04:40.700 --> 04:41.270 All right. 57 04:41.270 --> 04:48.590 So all we have to do to add inputs to our function is just to put the names of these parameters inside 58 04:48.590 --> 04:49.970 the parentheses. 59 04:49.970 --> 04:57.620 So now our function is able to take these parameters as inputs whenever this function gets called. 60 04:58.250 --> 05:03.650 The next step is we're going to convert these strings that get passed in, 61 05:03.650 --> 05:07.100 so it could be something like this all lowercase, 62 05:07.100 --> 05:11.210 it could be all capitalized, or it could be kind of random, right? 63 05:11.240 --> 05:14.240 Like some are capitalized, some are not. 64 05:14.270 --> 05:17.090 But we're going to make it all uniform. 65 05:17.090 --> 05:20.210 So all of these are going to end up like this. 66 05:20.210 --> 05:24.380 And to do this we can search around in Google, 67 05:24.380 --> 05:28.730 and you might come across a similar question in StackOverflow. 68 05:28.760 --> 05:32.810 "How do you convert a string to Title Case in Python?" 69 05:32.840 --> 05:34.250 They have an example, 70 05:34.250 --> 05:38.030 and it's trying to do exactly what we're trying to do. 71 05:38.060 --> 05:44.540 If we take a look at the answers, you can see that somebody is helpfully pointing to this title() 72 05:44.540 --> 05:45.290 function. 73 05:45.290 --> 05:52.040 So you take a string and then you write .title(), and then afterwards the string gets transformed 74 05:52.040 --> 05:56.480 and every word now starts off with a capital letter. 75 05:57.140 --> 06:03.290 And if you want to know more about how this title case works, then you can click on that link in title 76 06:03.290 --> 06:06.560 and then have a read through the Python documentation. 77 06:07.490 --> 06:15.530 Once you've read through that, go ahead and modify this f_name and l_name, so that they end up being 78 06:15.530 --> 06:17.510 both in title case. 79 06:17.540 --> 06:19.520 Pause the video and give that a go. 80 06:22.010 --> 06:22.640 All right. 81 06:22.640 --> 06:25.460 So we want to go ahead and take this f_name, 82 06:25.460 --> 06:26.960 and then write a dot, 83 06:26.960 --> 06:31.820 and then write title (.title), to convert it to title case. 84 06:31.850 --> 06:36.770 Once we've done that then we're going to do the same with the l_name. 85 06:37.700 --> 06:41.690 And if we go ahead and actually print these out... 86 06:42.620 --> 06:47.270 And of course in order for the function to actually execute, we'll have to call the function. 87 06:47.270 --> 06:49.940 So I'm going to put two inputs in here, 88 06:49.940 --> 06:54.960 one which is going to be just angela, all in lowercase, 89 06:54.990 --> 06:58.350 and then the second one is going to be ANGELA, 90 06:58.380 --> 06:59.670 all in uppercase. 91 06:59.700 --> 07:06.690 And now when I run this code, you'll see that the result is they both get converted to title case. 92 07:06.810 --> 07:14.430 In essence, this part of the code becomes whatever the previous value of f_name is, converted to title case. 93 07:15.000 --> 07:21.300 You might have spotted already that this title() function actually has an output. 94 07:21.330 --> 07:29.220 It returns a version of the string where each word is title cased. Instead of simply just printing 95 07:29.220 --> 07:29.670 this, 96 07:29.700 --> 07:33.060 we can also capture it inside a variable. 97 07:33.090 --> 07:45.660 Let's create a new variable called formatted f_name, and also formatted l_name. 98 07:46.350 --> 07:56.160 Now what's happening here is we are transforming this input f_name, turning it into title case, 99 07:56.160 --> 08:04.500 and then once this function executes, it has an output, and that output replaces this part of the 100 08:04.500 --> 08:05.160 code. 101 08:05.160 --> 08:08.970 And then it gets stored inside this variable. 102 08:09.330 --> 08:15.690 Now we can go ahead and print the final version of our function, which is going to use an f-string 103 08:15.720 --> 08:26.820 to take the formatted f_name, and then add a space, and then print out the formatted l_name like this. 104 08:26.880 --> 08:35.850 Now if I start out with my first name, but all in strange sort of casing, and then my last name in 105 08:35.850 --> 08:39.720 all caps, let's go ahead and hit Run and see what happens. 106 08:39.750 --> 08:45.540 You can see that my first name gets converted to title case, my last name gets converted to title case, 107 08:45.540 --> 08:49.260 and then that result is stored in formatted f_name. 108 08:49.260 --> 08:56.590 And this result becomes stored in this l_name, and then they get printed and formatted like so. 109 08:57.430 --> 09:05.920 Now instead of printing this result out, we could also return it as well, in the same way that this 110 09:05.920 --> 09:11.290 title function returns, the output replaces this part of the code, 111 09:11.290 --> 09:15.310 we can also do the same with our format_name() function. 112 09:15.310 --> 09:21.340 So let's delete the print function and go ahead and use return instead. 113 09:22.000 --> 09:26.050 Now this formatted string becomes the output. 114 09:26.050 --> 09:34.270 And as we mentioned before what happens with functions with outputs is this output replaces the part 115 09:34.270 --> 09:37.270 of the code where the function was called. 116 09:37.300 --> 09:45.820 Now if this is the string that we want to print, then all we have to do is just to save the output 117 09:45.820 --> 09:51.140 which replaces this part of the code inside a variable like this. 118 09:51.140 --> 09:57.350 And then all we have to do is just go ahead and print that formatted_string. 119 09:57.620 --> 10:01.430 As you can see, when I run the code, the same thing happens. 120 10:01.430 --> 10:09.350 Now you can and you might have alternatively just taken this function call and put it straight inside 121 10:09.350 --> 10:10.430 the print statement. 122 10:10.430 --> 10:12.860 That works exactly the same way, 123 10:12.860 --> 10:15.980 and we can visualize this using Thonny. 124 10:16.010 --> 10:26.000 If I go ahead and paste everything we have inside the editor and go ahead and run Debug, then we can 125 10:26.000 --> 10:29.840 step into and see what are the steps that happen. 126 10:29.840 --> 10:37.730 So the first thing when this Line 6 gets executed, is it tries to call this function format_name(). 127 10:37.730 --> 10:40.880 So it passes in these two inputs. 128 10:41.510 --> 10:48.890 And we're now within the function where we have access to these two inputs f_name and l_name. 129 10:48.980 --> 10:55.520 Now the formatted_f_name becomes the title case version of the first name, and the same thing happens 130 10:55.520 --> 10:56.720 with the last name. 131 10:56.720 --> 11:03.830 So we now have a formatted_f_name and a formatted_l_name, and that is what's going to be returned as 132 11:03.830 --> 11:04.940 the output. 133 11:05.840 --> 11:13.190 Now, once that's completed, that output replaces whatever was in between the print statement, which 134 11:13.190 --> 11:15.680 is where we called this format_name() function. 135 11:15.680 --> 11:18.890 And this is what gets printed into the console. 136 11:19.100 --> 11:25.130 As I mentioned before, we've actually already been using functions that we didn't create that have 137 11:25.130 --> 11:27.140 all of these functionalities, right? 138 11:27.140 --> 11:32.330 For example, the len() function takes an input and has an output. 139 11:32.330 --> 11:35.450 The input is going to be a string, 140 11:35.450 --> 11:39.320 my name again, I seem to be really obsessed with my own name. 141 11:39.980 --> 11:45.230 So now this line of code is going to run this built-in len() function, 142 11:45.230 --> 11:51.120 calculating the number of letters inside this input that we've given it, and then it's going to return 143 11:51.120 --> 11:56.430 the result as an output, which we can now capture inside a variable. 144 11:56.610 --> 11:58.530 This is the input. 145 11:58.530 --> 12:00.480 This is the function. 146 12:00.480 --> 12:09.390 And once this is completed the return or whatever it is after the return statement is going to replace 147 12:09.390 --> 12:11.190 this part of the code, 148 12:11.220 --> 12:16.350 then that result or output then gets stored inside this variable. 149 12:17.160 --> 12:23.370 So this return keyword is really the most important thing in order to create a function that has an 150 12:23.370 --> 12:30.000 output, because everything that comes after it is going to replace where the function was called. 151 12:30.030 --> 12:37.710 Now students often ask me, well, what is the difference then between a print statement and the output? 152 12:37.710 --> 12:43.740 Because it seems like we could use either to get to print to the output area. 153 12:43.890 --> 12:46.800 Well, here is the explanation 154 12:46.800 --> 12:53.730 if you also have this question in mind right now. Let's consider that we create a different function, 155 12:53.730 --> 12:57.330 and this function doesn't actually print its output at all. 156 12:57.330 --> 13:01.140 So let's define a function called function_1(), 157 13:01.140 --> 13:04.410 and it takes some text as input. 158 13:04.410 --> 13:11.940 And all it does is it outputs the original text, but it adds the original text together. 159 13:11.940 --> 13:20.640 So this way if I had the word for example, "hello", then the output would become "hellohello" like an 160 13:20.640 --> 13:21.450 echo. 161 13:21.600 --> 13:27.060 So now if I go ahead and create another function, let's call it function_2(), 162 13:27.060 --> 13:30.090 and it also takes some text as input, 163 13:30.120 --> 13:37.500 well in this case, this function_2() is going to return the text, but it's going to return it in title 164 13:37.500 --> 13:38.280 case. 165 13:38.280 --> 13:42.450 So we've already seen this before and we know how this works. 166 13:42.450 --> 13:44.850 It's going to take whatever input it is here, 167 13:44.850 --> 13:46.800 make the first letter capitalized 168 13:46.840 --> 13:49.300 and the rest of the letters lowercase. 169 13:49.300 --> 13:52.750 So neither of these functions have a print statement. 170 13:52.750 --> 13:57.790 So let's go ahead and call our first function and pass 171 13:57.790 --> 14:00.400 in a word let's say, "hello". 172 14:01.090 --> 14:05.620 Now we can save this to an output variable, 173 14:05.620 --> 14:08.350 and then go ahead and print it. 174 14:08.830 --> 14:13.420 Now you'll see I have that echo thing that I told you about earlier. 175 14:13.450 --> 14:15.430 But now here's the key part, 176 14:15.460 --> 14:26.140 what if, if we take the output of this function_1 and we use it as an input into function_2, how 177 14:26.140 --> 14:27.250 would we do that? 178 14:27.280 --> 14:33.070 Well, we know that the output of function_1, this is in fact a string, 179 14:33.070 --> 14:34.810 and it is a piece of text. 180 14:34.810 --> 14:38.950 So we can then put it into function2 as the input. 181 14:38.950 --> 14:44.230 And we would do it like this function2(), and then brackets, 182 14:44.260 --> 14:50.590 and so now the output of function_1 becomes the input for function_2, 183 14:50.620 --> 14:54.280 and then that input is then title cased. 184 14:54.280 --> 15:01.690 So now if we run our code you'll see that not only do we have the Hellohello functionality being carried 185 15:01.690 --> 15:06.820 out, we've also got the final text capitalized at the beginning. 186 15:07.240 --> 15:09.850 So that's pretty interesting right? 187 15:09.880 --> 15:16.690 We're only able to do this because we understand how the return function works. 188 15:16.690 --> 15:19.990 And we've got two functions that have outputs. 189 15:19.990 --> 15:25.960 And we've effectively chained the output of one function into the input of another one. 190 15:25.990 --> 15:29.440 Now this might mess with your head a little bit, so don't worry. 191 15:30.310 --> 15:35.350 In the next lesson, we'll take a quick look at the return keyword in more detail. 192 15:35.380 --> 15:41.770 Specifically, let's see what happens when we have more than one return statement in the same function. 193 15:41.800 --> 15:44.920 All right, for all of that and more, I'll see you there.