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So, before we get too far into
the mechanics of programming,

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let's talk about the biggest
subject of all design.

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I don't mean how your software looks
on a website or a phone, though.

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I'm talking about the organization
thinking and layout of your code.

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In previous courses, most of our
code has been in a single file.

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This is fine for
small amounts of code, but

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you'll quickly see that we don't
always have small code footprints.

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Libraries and tools can quickly
reach hundreds, if not thousands,

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of lines of code.

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That's just not something you
want to read all in one file.

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We've all been there, right,
a document that just keeps scrolling and

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scrolling and scrolling.

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Now, imagine you're on line
595 of some script and

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see a function reference from
all the way up at line 18.

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IDEs and other editors can
reduce the amount of scrolling,

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but wouldn't it be better if
you didn't have to do that?

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And this is the first case
that software design solves.

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Well, it helps at least.

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We can break our code up into modules or
files.

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By putting code into logical groupings we
can make it easier to take it all in and

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think about what we need
to do to do our job.

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This logical grouping
goes even further though.

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We already grouped related lines
of code together into functions.

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Now with classes we have
another layer of grouping.

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If you have multiple functions that all
work together think about putting them

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into a class.

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OOP provides us with so many tools that
it's often hard to know which ones to use,

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or, if you should even use any of them.

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I don't want to just
dump a ton of terms and

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features on you, so, I'll be bringing
them up as we go through the course.

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I'll also be talking about how to use and

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think about these features in
the design of your software.

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But I can only influence your thinking so
far.

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I need you to also consider how
you'd use each of these things

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in the design of your own software.

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An often overlooked truth of software
development is that there's rarely any

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one correct way to solve a problem or

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design an algorithm, so like I said
this organization starts at its

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barest of bones with organizing
code into functions and classes.

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Let's think back to the shopping list
app that we built in Python basics and

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Python collections.

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[SOUND] We had a list that held
the things we wanted to shop for,

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we had functions to add things to
the list, reorganize the list,

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and remove things we didn't need or
had already bought.

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Well right there I see something
that makes sense for a class,

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the ShoppingList itself.

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I can see going a step further though and
making each thing on the list and

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instance of some other class.

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Maybe this class would hold the name for

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the thing, how many that I wanted,
what store it was at, who knows.

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There are many options for
the functionality of this class.

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And that brings me to another point,
ruthless editing.

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As you build classes and
methods and functionality,

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keep in mind a very common acronym, YAGNI,
which stands for, you ain't gonna need it.

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Keep your code lean and mean and
you'll find it easier to use and

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better for building awesome things with.

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It's always a good idea to keep it
simple or as the Zen of Python says,

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if implementation is hard to explain, it's
a bad idea. Often you'll find that you can

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approach software design like you would
the design of something in the real world.

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Just like you wouldn't add a fish
radar to your screwdriver,

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you probably shouldn't add a function
to send email to your calculator app,

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practicality and logical thinking will
lead to better software every time.

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As part of that practicality, remember
you're writing Python not Java or C# or

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any other language.

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If you come to Python from one of those
languages, you might expect me to talk

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about getters and setters or
access controls on methods and attributes.

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Python doesn't rely on
these design features.

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And you'll rarely find a place where
they're absolutely needed in Python.

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Stick to writing simple, clean code and
as little code as possible,

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and you'll find yourself
a happier programmer.

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All right, I think that's enough
talking about design for now.

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Go back and look at the code we've
written together previously and

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see if you can find places
to add simple classes.

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Even if you can't add them right now,
keep those places in mind for

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when you hit further through this course.

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I'm sure you'll find all sorts of
places to improve our old code.

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Now though,
let's get into the fun stuff and

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start talking about the real wealth of
object oriented design, inheritance.