1 00:00:00,490 --> 00:00:03,850 To get started we're going to learn more about functions. 2 00:00:04,330 --> 00:00:09,330 And previously we learned that functions are a really handy way of taking a 3 00:00:10,540 --> 00:00:15,540 complex set of instructions and packaging them together inside a block of code 4 00:00:17,470 --> 00:00:19,540 that has a name given to it. 5 00:00:20,080 --> 00:00:24,580 And when we need all of the lines of code that's packaged inside this 6 00:00:24,580 --> 00:00:25,390 function, 7 00:00:25,390 --> 00:00:30,390 all we have to do at any point later on in our code is just to call the function 8 00:00:30,940 --> 00:00:34,030 by typing its name and then a set of parentheses. 9 00:00:34,750 --> 00:00:36,760 And when this line of code is run, 10 00:00:37,030 --> 00:00:41,440 it's going to search for where this function is defined, which is up here, 11 00:00:41,830 --> 00:00:45,490 and then it's going to execute all the lines of code that are contained within 12 00:00:45,490 --> 00:00:49,330 it. Now it's been a little while since we've seen functions. 13 00:00:49,390 --> 00:00:54,390 So I want you to go ahead and find the starting replit for day 8 14 00:00:55,030 --> 00:00:56,470 which is at this URL 15 00:00:56,680 --> 00:01:01,270 and then fork it to create your own copy. To begin, 16 00:01:01,330 --> 00:01:04,569 I want you to create a new function called greet, 17 00:01:05,110 --> 00:01:08,110 and I want you to give it three lines of print statements, 18 00:01:08,350 --> 00:01:12,220 telling it to do three things. And finally, once you're done, 19 00:01:12,250 --> 00:01:16,630 go ahead and call the function so that it gets executed in the console. 20 00:01:16,900 --> 00:01:20,560 So pause the video and give that a go. All right. 21 00:01:20,560 --> 00:01:23,770 So to create a function, we of course need a def keyword. 22 00:01:24,130 --> 00:01:26,710 And we know it's a keyword, because as soon as we type it, 23 00:01:26,770 --> 00:01:30,790 it changes to the blue color. And after the key word, 24 00:01:30,850 --> 00:01:35,170 we get to give our function a name. So in my case, it's called greet. 25 00:01:35,860 --> 00:01:40,630 Now after the greet, we add a set of parentheses after the name of the function. 26 00:01:41,530 --> 00:01:42,363 Finally, 27 00:01:42,430 --> 00:01:47,430 we add a colon and we enter into the block of code because we're indented over. 28 00:01:48,880 --> 00:01:49,390 Now, 29 00:01:49,390 --> 00:01:52,840 the first thing I'm going to do is to create a print statement that just says 30 00:01:52,840 --> 00:01:55,720 Hello. And then I'm going to say, well, 31 00:01:56,200 --> 00:02:00,460 how do you do? Nobody in England actually says this, 32 00:02:00,790 --> 00:02:04,990 but I always see it in the learn English books, which is quite funny. 33 00:02:05,440 --> 00:02:07,120 I think people will give you a very strange look 34 00:02:07,150 --> 00:02:11,980 if you go to somebody at the bakery and say, well, how do you do? But anyways, 35 00:02:12,880 --> 00:02:16,600 now finally, we're going to add a final print statement, 36 00:02:17,050 --> 00:02:21,670 keeping in line with the Britishness of my function, 37 00:02:22,090 --> 00:02:23,710 going to ask about the weather. 38 00:02:24,940 --> 00:02:29,770 Now this line, on the other hand, is something that you will often hear a British 39 00:02:29,770 --> 00:02:32,080 people say. They're obsessed about the weather, 40 00:02:32,350 --> 00:02:34,750 mostly because it's terrible all the time. 41 00:02:35,500 --> 00:02:37,930 So now that we've created our function, 42 00:02:37,930 --> 00:02:42,100 it's time to actually trigger the function or what we see in programming lingo, 43 00:02:42,400 --> 00:02:43,540 call the function. 44 00:02:43,900 --> 00:02:48,100 And we do that by calling the name of the function and then adding a set of 45 00:02:48,100 --> 00:02:51,940 parentheses. And now once the code reaches line six 46 00:02:51,970 --> 00:02:55,750 it's going to search for this greet function, which it'll find over here 47 00:02:56,050 --> 00:02:59,590 and then it's going to carry out each of the lines of code one by one. 48 00:03:00,040 --> 00:03:04,000 So let's run the code and you should see each of the three print statements 49 00:03:04,060 --> 00:03:06,730 being called. So that's pretty simple. 50 00:03:08,470 --> 00:03:12,100 Notice that every single time I call the greet function, 51 00:03:12,640 --> 00:03:15,190 it's going to do the same thing, right? 52 00:03:15,190 --> 00:03:19,630 It's just going to print out those three lines of code. Now, in reality, 53 00:03:19,630 --> 00:03:24,630 it's very rare that you'll want to repeat the same instructions every single 54 00:03:24,790 --> 00:03:28,090 time when you call a function. It would be nice, wouldn't it, 55 00:03:28,110 --> 00:03:33,110 if we could modify some of the parts of the code inside the function and allow 56 00:03:34,030 --> 00:03:36,790 for a little bit of variation. For example, 57 00:03:36,790 --> 00:03:40,600 it would be nice if we could greet somebody by the name so that it could say, 58 00:03:40,900 --> 00:03:45,580 hello Angela, instead of just, hello. How do you do Angela? 59 00:03:45,910 --> 00:03:49,480 So that it could change each time I call this function. 60 00:03:49,570 --> 00:03:53,860 Maybe next time it will be, how do you do Jack Bauer, et cetera. 61 00:03:54,130 --> 00:03:58,390 So how can we achieve this kind of functionality? Well, 62 00:03:58,390 --> 00:04:01,600 we need to look more closely at these parentheses. 63 00:04:02,200 --> 00:04:07,200 Now what we can do is we can actually add the name of a variable inside those 64 00:04:08,800 --> 00:04:12,520 parentheses to start giving our functions some inputs. 65 00:04:12,970 --> 00:04:17,079 So let's say that there's a variable called something that's going to be passed 66 00:04:17,110 --> 00:04:22,110 to my function. And this something can then be used inside this block of code, 67 00:04:24,610 --> 00:04:25,443 this function. 68 00:04:25,900 --> 00:04:30,520 And I could do something with it. Now in order to actually pass this value 69 00:04:30,520 --> 00:04:35,380 when I call my function, I have to add the data inside the parentheses. 70 00:04:35,650 --> 00:04:39,910 So let's say I decide to pass 123 over, well 71 00:04:39,910 --> 00:04:43,120 in this case, when this line of code gets triggered, 72 00:04:43,570 --> 00:04:46,990 the computer is going to search for where this function is declared, 73 00:04:47,020 --> 00:04:51,940 which is up here, and then it's going to pass over this piece of data, 74 00:04:52,300 --> 00:04:56,080 123, over to this variable called something. 75 00:04:56,620 --> 00:05:00,940 So now, effectively, inside this function called my_function, 76 00:05:01,240 --> 00:05:05,680 we now have a variable called something that's equal to 123 77 00:05:06,400 --> 00:05:11,400 and that can then be used inside the block of code to do something with that 78 00:05:11,410 --> 00:05:12,243 piece of data. 79 00:05:14,470 --> 00:05:18,220 Now it's a bit like plugging in a USB stick into a computer. 80 00:05:18,790 --> 00:05:21,100 If we took a different piece of input, 81 00:05:21,190 --> 00:05:25,450 we would end up with a different file being shown by the computer. 82 00:05:25,900 --> 00:05:30,900 So this means the computer can do something different depending on the input that 83 00:05:31,390 --> 00:05:33,880 we give it. And if we change that input, 84 00:05:34,000 --> 00:05:36,280 then it will receive a different piece of data. 85 00:05:37,180 --> 00:05:39,700 So in addition to a simple function, 86 00:05:39,730 --> 00:05:43,060 we can also create a function that allows for input. 87 00:05:44,140 --> 00:05:49,140 And to do that you saw earlier on the syntax is again the same as before we use 88 00:05:49,690 --> 00:05:51,940 a Def to create the function. 89 00:05:52,360 --> 00:05:56,230 And then let's just give it a slightly different name to differentiate it with 90 00:05:56,230 --> 00:05:59,150 the previous function, greet_with_name. 91 00:05:59,720 --> 00:06:03,650 And then inside the parentheses, instead of leaving it blank, 92 00:06:03,890 --> 00:06:07,550 we get to create the name of the variable that's going to be passed over. 93 00:06:08,000 --> 00:06:12,170 So let's just call it name because that describes the data that's going to be 94 00:06:12,170 --> 00:06:15,770 received. It's going to be the name of the person that I wish to greet. 95 00:06:16,340 --> 00:06:21,140 So now let's add a colon and finally we can create our print statements. 96 00:06:21,740 --> 00:06:25,640 So I'm just going to copy these print statements from above and now, 97 00:06:25,670 --> 00:06:30,530 instead of having these names hard coded in here, I'm going to delete it 98 00:06:30,680 --> 00:06:35,680 and I'm going to replace those names with the value of this variable. 99 00:06:36,110 --> 00:06:40,130 So I'm going to put it in using an fstring like this, 100 00:06:40,580 --> 00:06:43,250 and then I'm going to do the same down here. 101 00:06:46,740 --> 00:06:47,573 Right? 102 00:06:47,910 --> 00:06:49,740 When we actually call this function, 103 00:06:49,770 --> 00:06:53,430 it's also going to be a little bit different from previously on line six. 104 00:06:53,970 --> 00:06:57,180 So now firstly, the name of the function has changed. 105 00:06:57,630 --> 00:07:02,630 But notice how it's expecting some sort of input inside the parentheses. 106 00:07:03,120 --> 00:07:05,640 And it tells me that it wants to receive a name. 107 00:07:06,180 --> 00:07:10,830 It's when we call the function that we actually pass over the piece of data 108 00:07:10,860 --> 00:07:15,570 that's going to be stored inside this variable. Let's give it my own name, 109 00:07:15,900 --> 00:07:19,110 Angela. And now when I hit run, 110 00:07:19,470 --> 00:07:21,420 I want you to predict what's going to happen, 111 00:07:21,450 --> 00:07:23,190 what's actually going to be printed. 112 00:07:23,400 --> 00:07:28,400 So let's go ahead and comment out the previous line of code and now run our code. 113 00:07:30,240 --> 00:07:34,020 And you should see that it says, hello Angela, how do you do Angela.? 114 00:07:34,020 --> 00:07:38,610 So this piece of data has basically been inserted under this variable name 115 00:07:38,910 --> 00:07:42,810 and then it's been put into both of these print statements. Now, 116 00:07:42,810 --> 00:07:47,100 if I go ahead and call this function with a different piece of data, 117 00:07:47,760 --> 00:07:49,230 say a different name, 118 00:07:49,650 --> 00:07:54,060 then it's going to use that piece of data to modify this function 119 00:07:54,300 --> 00:07:56,580 so it does something a little bit different. 120 00:07:57,090 --> 00:08:02,010 So this way we can create one function that carries out some instructions, 121 00:08:02,310 --> 00:08:06,240 but every time we execute it, it gets a modify it a little bit 122 00:08:06,510 --> 00:08:08,340 by changing the inputs. 123 00:08:09,360 --> 00:08:11,760 When we're talking about functions with inputs, 124 00:08:12,030 --> 00:08:13,950 there's two things that we're working with 125 00:08:13,980 --> 00:08:16,200 that's really important to differentiate. 126 00:08:17,190 --> 00:08:22,170 So we know that when we call this function and we pass over this piece of data, 127 00:08:22,500 --> 00:08:23,460 effectively 128 00:08:23,490 --> 00:08:28,490 we're creating a new variable called something and we're setting it to equal this 129 00:08:28,860 --> 00:08:33,030 piece of data that we're passing it. Now in programming lingo, 130 00:08:33,059 --> 00:08:38,059 you'll hear this being referred to as the parameter and this piece of data 131 00:08:38,460 --> 00:08:42,240 being referred to as the argument. Now, 132 00:08:42,240 --> 00:08:45,000 the argument is the actual piece of data 133 00:08:45,030 --> 00:08:49,110 that's going to be passed over to this function when it's being called. 134 00:08:49,560 --> 00:08:52,920 Whereas the parameter is the name of that data 135 00:08:53,340 --> 00:08:57,990 and we use the parameter inside the function to refer to it and to do things 136 00:08:57,990 --> 00:09:01,620 with it. Now very often on the internet when you come across 137 00:09:01,620 --> 00:09:03,090 somebody explaining something 138 00:09:03,090 --> 00:09:06,060 be it on Stack Overflow or in some piece of documentation, 139 00:09:06,420 --> 00:09:09,600 you'll hear them referring to these two types of things, 140 00:09:09,600 --> 00:09:11,550 the parameter and the argument. 141 00:09:12,090 --> 00:09:15,930 So if you need to, come back to this lesson and remind yourself the difference 142 00:09:15,930 --> 00:09:17,160 between those two things. 143 00:09:17,550 --> 00:09:20,550 The parameter is the name of the data that's being passed in, 144 00:09:20,850 --> 00:09:24,990 the argument is the actual value of the data. Now, 145 00:09:25,020 --> 00:09:28,770 sometimes people also get confused on the internet between these two words, 146 00:09:29,040 --> 00:09:32,010 but as long as you know what they means, then you'll be in a good place.