1 00:00:00,330 --> 00:00:07,620 Earlier in the course we were looking for a mean or an average function that Python might have to allow 2 00:00:07,620 --> 00:00:12,970 us to make the average of the items of the numbers of a list. 3 00:00:13,020 --> 00:00:19,980 And we found out that Python has some more fundamental functions such as len to get the number of items 4 00:00:19,980 --> 00:00:26,520 of a list and sum to make the sum of the numbers of the list but it doesn't have a mean function. 5 00:00:26,550 --> 00:00:28,410 So we ended up doing this. 6 00:00:28,410 --> 00:00:33,330 So we had this list we calculated the sum using the sum function calculated the length. 7 00:00:33,330 --> 00:00:39,660 So that number of items using the lend function and then did the division between sum and len to get them 8 00:00:39,660 --> 00:00:40,560 mean. 9 00:00:40,560 --> 00:00:48,750 However the fact that Python doesn't have a mean function doesn't mean we cannot create our own mean 10 00:00:48,750 --> 00:00:49,230 function. 11 00:00:49,470 --> 00:00:56,130 So what we are we going to do now is we're going to create our own mean function. To create functions 12 00:00:56,130 --> 00:01:01,050 in Python you use the def keywords and then pick a name for your function. 13 00:01:01,150 --> 00:01:07,560 The name has to follow the same naming rules as with variables so it cannot start with the number, 14 00:01:07,560 --> 00:01:09,960 it cannot start with a math operator. 15 00:01:09,960 --> 00:01:17,970 So let's say you mean, then you use round parentheses and inside those and the first line ends with 16 00:01:18,090 --> 00:01:26,310 colon and inside the parentheses optionally you can input some parameters of your function. 17 00:01:26,310 --> 00:01:29,870 Parameters in other words is the input that your function will get. 18 00:01:30,090 --> 00:01:34,140 And that will process that's input and that will produce an an output, the input 19 00:01:34,140 --> 00:01:36,800 in our case it would be a list. 20 00:01:36,870 --> 00:01:39,330 However here you have to give a name following 21 00:01:39,330 --> 00:01:41,820 again the same rules as with variables. 22 00:01:42,190 --> 00:01:44,440 Let's say mylist. 23 00:01:44,530 --> 00:01:52,170 Okay, then you want to press enter there and you see that's automatically Visual Studio code, 24 00:01:52,260 --> 00:01:56,410 so the editor indented the next line with four spaces. 25 00:01:56,580 --> 00:01:58,410 One,, two, three, four. 26 00:01:59,520 --> 00:02:02,970 So that's what the syntax requires that after the first line. 27 00:02:03,300 --> 00:02:09,390 So after you have defined what name you want for your function and what parameters you want, you 28 00:02:09,390 --> 00:02:12,560 have to indent the next two lines. 29 00:02:12,810 --> 00:02:18,930 So either your editor will do it automatically, but if it doesn't do it one, two, three, four. 30 00:02:19,170 --> 00:02:21,300 Just indents four spaces in there. 31 00:02:21,360 --> 00:02:29,610 You can also make it with one space, so just one space would also work plus it's recommended to use 32 00:02:29,610 --> 00:02:35,240 four spaces, everyone uses for spaces because it's more visible the indented code. 33 00:02:35,370 --> 00:02:42,810 So it will make your code more readable and then you can start to calculate the mean, let's say the_mean. 34 00:02:43,290 --> 00:02:50,940 I'm going to call it like that so I don't confuse it with the function name, that would be the sum of my 35 00:02:51,660 --> 00:03:00,420 list divided by the length of my list and next. 36 00:03:00,420 --> 00:03:07,740 What we want to do we want to use the return keyword and that is followed by what you want to return. 37 00:03:08,040 --> 00:03:09,700 Well we want to return the mean. 38 00:03:09,740 --> 00:03:17,580 Now save that, and let me open a terminal I want to execute these scripts now. 39 00:03:17,580 --> 00:03:20,460 So let me show you what will happen. 40 00:03:20,610 --> 00:03:22,860 Nothing will actually happen. 41 00:03:23,250 --> 00:03:28,470 Nothing happens because what Python does is it just reads this definition. 42 00:03:28,470 --> 00:03:33,270 This is like a blueprint. You have declared what your functions should do. 43 00:03:33,270 --> 00:03:38,550 But you didn't tell Python to execute your function. To execute your function 44 00:03:38,550 --> 00:03:40,920 you want to call the function, 45 00:03:43,640 --> 00:03:54,980 pass an input value for that parameter that you defined, and also you want to print out, print open parentheses 46 00:03:54,980 --> 00:04:01,670 there, close parentheses there, save don't forget, and execute. 47 00:04:01,700 --> 00:04:12,960 That's the mean of those three numbers, so like that I can easily try this out with many input values just 48 00:04:12,960 --> 00:04:17,310 like that I don't have to rewrite anything in here. 49 00:04:17,380 --> 00:04:19,130 That's the beauty of a function. 50 00:04:19,200 --> 00:04:22,540 So you can see the similarity here. 51 00:04:22,770 --> 00:04:29,600 Just like we use the sum function, we are using the mean function in the same way. 52 00:04:30,120 --> 00:04:35,680 So sum gets this input value, mean gets to this input value. 53 00:04:35,700 --> 00:04:36,890 This happens to be a variable. 54 00:04:36,890 --> 00:04:45,390 This happens to be a direct value, but it doesn't matter. If you check the type of mean, type mean, and 55 00:04:45,390 --> 00:04:53,920 type of sum what you're going to see is that mean is a function. 56 00:04:54,000 --> 00:05:04,860 So that was printed out, this was printed out by this, so mean is a function and sum is again a function, 57 00:05:04,890 --> 00:05:10,980 but it's a built in function so it's built in in the Python interpreter, It was designed by the python 58 00:05:11,490 --> 00:05:16,940 core development team and this function was designed by me, the programmer. 59 00:05:17,130 --> 00:05:21,920 So that is how you create and call a function in Python.