Functions

[MUSIC] 0:00 We've used some predefined functions throughout this course. 0:04 And they've proven to be super handy. 0:07 You know functions like print and input, we also used len. 0:09 Functions are great, they provide a way for 0:13 you to group multiple statements together to use later. 0:15 They help you avoid duplicating your code. 0:18 Now if you ever find yourself writing the same exact code more than once, 0:21 it's a symptom that something is likely wrong. 0:24 Now we refer to these symptoms as code smell, like hmm, 0:27 something about this code smells. 0:31 Here, let me help you write some smelly code and 0:33 then we'll clean it up with the power of functions. 0:35 Getting someone's attention these days is so hard. 0:38 In application development, you like have to bounce an icon or make a noise, 0:42 [SOUND] to alert them, right? 0:46 So one solution that we could do in our textual environment here is to yell in 0:48 all upper case. 0:53 And I feel like the more exclamation points, 0:54 the more likely they're gonna see it. 0:56 Let's do that, let's create some text and 0:58 then convert it to an upper cased and exclamatory phrase. 1:01 So I'm gonna make a new file actually, so let's go here, we'll go to File, 1:05 and then New File, and I'm gonna name it notifications.py. 1:10 So the first thing that I would love to shout from the rooftop 1:17 is some praise for you. 1:21 So, I'll assign it to the variable praise and 1:24 well say, "You are doing great". 1:27 So, we want to uppercase this, right? 1:32 And what we'll do is we'll just reassign it, so 1:34 we'll say praise = praise.upper. 1:38 And that's because strings are immutable and they can't be changed. 1:42 So it returns a brand new string, 1:45 which we're just going to take our label off the old one and put it on the new one. 1:47 Now I think there should be at least as many exclamation marks 1:51 as there are characters in the string, to really grab your attention. 1:54 So to get the numbers of characters in the string I can use the len function. 1:59 The len function expects an object, so we'll pass in our variable. 2:03 And then I'm gonna store that in a new variable called number_of_characters. 2:07 And I'm gonna call the len function, I'm gonna pass in our string, here we go. 2:16 So we wanna create a new value that is a combination of this praise and 2:22 the exclamation points. 2:27 So let's create a new variable called result. 2:28 And we'll make that praise and we'll concatenate the exclamation point. 2:33 And we're gonna rely on order of operations here so we'll say, 2:38 the exclamation point times the number_of_characters. 2:43 And then finally, we'll print that out. 2:47 And we'll run python notifications, cuz it's a new file. 2:55 There it is, YOU ARE DOING GREAT. 3:02 And you're doing great. 3:04 That's is some good looking code, and fine smelling too. 3:05 You know what, I also like to remind you that you should remember to ask for 3:08 help when you need it. 3:12 So can we yell that too, please? 3:15 I don't see why not, right? 3:17 So let's make a new variable, we'll call that advice and 3:19 that is, "Don't forget to ask for help". 3:24 And then, well I guess I would just copy this code, right? 3:28 Copy this code here, and paste it down here. 3:36 Guess I would change, I need to change this praise and make that advice. 3:41 And I make this advice. 3:46 Cuz it's the length of device, 3:50 not the length of praise because that's a different variable. 3:52 And then we do this, so basically I just copied and pasted that code and 3:55 changed this variable name. 4:00 That style of coding is called copy pasta, and it's not a good habit to fall into. 4:02 And it's really a bad habit, especially if you don't understand what the code 4:08 you've copied [LAUGH] is doing, it happens all the time. 4:12 So here we go, lets keep going. 4:16 You know what, I've got a another piece of advice for 4:19 you that I would love you to yell for me. 4:22 In coding, there's an acronym that we call dry or D-R-Y, don't repeat yourself. 4:24 Let's yell that. 4:32 So, I guess that's some more advice, right? 4:34 So let's call that advice2, and 4:35 we'll say, "Don't Repeat Yourself. 4:40 Keep things DRY". 4:46 Okay so, I guess I'll copy and pasta this. 4:49 We'll put this here and I'll go ahead and do advice2. 4:53 Advice2, the length of advice2, 4:58 and then we'll do advice2. 5:03 And then let's just make sure that this is working. 5:08 Okay, It is, but what if I told you that we had like ten more of these to do? 5:11 Would you be excited about that? 5:18 You know what, actually after seeing this in action, I'd like to make it so 5:20 that there are half as many. 5:23 This is [LAUGH], this is ridiculous. 5:24 That's way too many exclamation points. 5:27 So I wanna make only half of those as there are characters, right. 5:28 So half of the amount of characters we should do so. 5:32 One thing that I can think of doing is if we look we can make it so 5:35 that we use the floor division. 5:39 That was that the double division where we get an integer. 5:40 So we can, if we divide the number of characters by 2 and keep it an integer. 5:43 That should be that, and 5:48 I'm gonna put parens around here because I want the order of operations to work 5:49 correctly. 5:52 So let's go ahead, let's run that. 5:52 The first one looks great, but the other two don't seem to be. 5:55 Rats, I forgot to update those too. 6:00 Because my code is duplicated, it means any change that I need to make 6:03 I have to change every single place I copied and pasta-ed this code. 6:09 Well, that's really smelly right? 6:14 So let's clean up the smell, anybody got some Febreze? 6:17 [LAUGH] Totally missed product placement opportunity right there. 6:20 [LAUGH] I guess functions are definitely an air freshener for 6:24 these type of code smells. 6:28 So let's create one, shall we? 6:30 So the way that you create a function, let's get up here. 6:33 The way that you create a function is with the keyword named def, 6:37 which is short for define. 6:42 And then you give your function a name, let's name it yell. 6:44 That seems like exactly what we're doing, right, so we'll say yell. 6:48 And then when you're defining a function, 6:51 you define what parameters are expected when it's called. 6:53 So in this case, we want to accept the text that should be yelled. 6:57 Let's go ahead, and we'll call that text. 7:02 And then we add a colon, cuz we're gonna start the body of the function. 7:04 And you press Enter, and see how it's indented automatically here? 7:08 And now, we are in what is called the function body. 7:13 This is the code that is run when the yell function is called. 7:18 So we basically want to do exactly what we did in our previous code that we were 7:22 copying and pasting, right? 7:26 So let's just do that one more time, we're gonna copy this code here. 7:27 I'm gonna cut it out, when I come in here I'm gonna paste it. 7:32 And if you come in front of these lines and 7:35 press Tab, you can see that they tab into our body. 7:37 So instead of praise, this is now text. 7:40 I'm using Shift and the arrow key to do that highlighting. 7:44 You get better at those and you forget to say. 7:50 So that's how I'm doing that, so text. 7:52 That looks good, and 7:56 it's really good style to leave at least one space after your function definition. 7:58 So that it's clear that it's a function where it ends. 8:03 So now, we can go ahead and call that. 8:06 So let's do this, we'll get rid of this. 8:10 We won't assign it anymore, we'll say yell("You are doing great"). 8:13 And then we don't need this other code too, let's clean this up. 8:19 So we'll say yell("Don't forget to ask for help"). 8:21 And then finally, let's go call this last one here. 8:27 We'll say, yell("Don't Repeat Yourself. 8:31 Keep things DRY"), we'll get rid of these. 8:34 That looks a lot better, right? 8:38 Let's go ahead, let's run it and make sure things are working. 8:40 There we go, these lines are even shorter now, great. 8:45 So let's review what we've got. 8:48 So, we used the def keyword to define a new function named yell. 8:51 Yell declares a parameter which is named text. 8:58 This is the body of the function. 9:01 It's all this code that's indented four spaces by our style definition. 9:03 Now, the function body has code that upper cases and concatenates half-ish 9:07 the amount of text in the exclamation marks, and then it prints. 9:11 We've got a blank line after our function definition, 9:16 because we're adhering to good coding style. 9:19 It's important, right? 9:21 I want you to keep in mind that just defining this function 9:22 doesn't run the code. 9:25 What it does is it creates a new name of yell that we can call later, 9:27 and we can do it multiple times. 9:32 So here we're calling the yell method that we just created, and we're passing in 9:34 a brand new string that we just created that says "You are doing great". 9:38 So that's a brand new string. 9:42 And then the values that you push into a function are called arguments. 9:45 And since this is the first argument, right, there's only one. 9:49 It's the first argument here, and it's called text here. 9:53 So basically what this is saying, is text equals you are doing great. 9:57 That's what I want you to imagine. 10:01 So text equals you are doing great, and 10:03 then the rest of the code runs on you are doing great. 10:04 It runs through each one of these texts you are doing great, you are doing great. 10:09 Prints the result, and then it pops back out to whatever the next line is. 10:13 In this case, is another call to the yell function. 10:18 And we create a new string that says, don't forget to ask for help. 10:20 And imagine again, text equals, don't forget to ask for help. 10:23 And then the rest of the function runs, it pops out. 10:27 We get to the next one, yell, don't repeat yourself. 10:30 So on and so forth, I feel like I'm repeating myself. 10:34 Now also if we wanted to change the way that this yell function worked, 10:37 we only need to change it in one place. 10:41 Like for instance, I think even this too is a little long. 10:44 Why don't we do it to a fourth of that? 10:48 So if I come up in here, 10:50 I can just change this in one place now and all of those functions run. 10:52 Functions are pretty handy aren't they? 10:57 We've just scratched the surface of how powerful these functions can be. 11:00 But, they definitely help you to create nice reusable code. 11:04 And try to stay on the lookout for lines of code that are repeated. 11:08 Recognize the code smell. 11:12 Don't repeat yourself is a great mantra to live by. 11:14 It will lead you to write clean, understandable, and maintainable code. 11:16 Everyone can agree that repeating what you're saying over and 11:21 over is super annoying. 11:25 Everyone can agree that repeating what you're saying over and 11:27 over is super annoying. 11:30 Everyone can agree that repeating what, right. 11:32 Keep things DRY everybody. 11:35