Design

So, before we get too far into the mechanics of programming, 0:00 let's talk about the biggest subject of all design. 0:04 I don't mean how your software looks on a website or a phone, though. 0:07 I'm talking about the organization thinking and layout of your code. 0:09 In previous courses, most of our code has been in a single file. 0:14 This is fine for small amounts of code, but 0:17 you'll quickly see that we don't always have small code footprints. 0:19 Libraries and tools can quickly reach hundreds, if not thousands, 0:23 of lines of code. 0:26 That's just not something you want to read all in one file. 0:27 We've all been there, right, a document that just keeps scrolling and 0:30 scrolling and scrolling. 0:32 Now, imagine you're on line 595 of some script and 0:34 see a function reference from all the way up at line 18. 0:38 IDEs and other editors can reduce the amount of scrolling, 0:41 but wouldn't it be better if you didn't have to do that? 0:43 And this is the first case that software design solves. 0:45 Well, it helps at least. 0:49 We can break our code up into modules or files. 0:50 By putting code into logical groupings we can make it easier to take it all in and 0:53 think about what we need to do to do our job. 0:57 This logical grouping goes even further though. 1:00 We already grouped related lines of code together into functions. 1:02 Now with classes we have another layer of grouping. 1:05 If you have multiple functions that all work together think about putting them 1:07 into a class. 1:10 OO provides us with so many tools that it's often hard to know which ones to use, 1:12 or, if you should even use any of them. 1:16 I don't want to just dump a ton of terms and 1:18 features on you, so, I'll be bringing them up as we go through the course. 1:20 I'll also be talking about how to use and 1:23 think about these features in the design of your software. 1:25 But I can only influence your thinking so far. 1:27 I need you to also consider how you'd use each of these things 1:30 in the design of your own software. 1:32 An often overlooked truth of software development is that there's rarely any 1:34 one correct way to solve a problem or 1:38 design an algorithm, so like I said this organization starts at its 1:40 barest of bones with organizing code into functions and classes. 1:45 Let's think back to the shopping list app that we built in Python basics and 1:48 Python collections. 1:51 [SOUND] We had a list that held the things we wanted to shop for, 1:52 we had functions to add things to the list, reorganize the list, 1:55 and remove things we didn't need or had already bought. 1:58 Well right there I see something that makes sense for a class, 2:01 the ShoppingList itself. 2:04 I can see going a step further though and making each thing on the list and 2:05 instance of some other class. 2:08 Maybe this class would hold the name for 2:10 the thing, how many that I wanted, what store it was at, who knows. 2:11 There are many options for the functionality of this class. 2:14 And that brings me to another point, ruthless editing. 2:19 As you build classes and methods and functionality, 2:22 keep in mind a very common acronym, YAGNI, which stands for, you ain't gonna need it. 2:24 Keep your code lean and mean and you'll find it easier to use and 2:29 better for building awesome things with. 2:33 It's always a good idea to keep it simple or as the Zen of Python says, 2:34 if implementation is hard to explain, it's a bad idea often you'll find that you can 2:38 approach software design like you would the design of something in the real world. 2:43 Just like you wouldn't add a fish radar to your screwdriver, 2:46 you probably shouldn't add a function to send email to your calculator app, 2:48 practicality and logical thinking will lead to better software every time. 2:52 As part of that practicality, remember you're writing Python not Java or C# or 2:56 any other language. 3:00 If you come to Python from one of those languages, you might expect me to talk 3:02 about getters and setters or access controls on methods and attributes. 3:04 Python doesn't rely on these design features. 3:09 And you'll rarely find a place where they're absolutely needed in Python. 3:10 Stick to writing simple, clean code and as little code as possible, 3:14 and you'll find yourself a happier programmer. 3:16 All right, I think that's enough talking about design for now. 3:19 Go back and look at the code we've written together previously and 3:22 see if you can find places to add simple classes. 3:24 Even if you can't add them right now, keep those places in mind for 3:27 when you hit further through this course. 3:29 I'm sure you'll find all sorts of places to improve our old code. 3:31 Now though, let's get into the fun stuff and 3:34 start talking about the real wealth of object oriented design, inheritance. 3:36