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So, it's

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Monty Python Flying Circus

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okay actually it is not but just so you know

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this is where the python language got its name

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it is from the comedy
but today's talk will be about OOP or object-orientated programming in python

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And I am Junxi, I am a second-year student from Singapore University of Technology and Design

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currently in the Computer Science / info systems major

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And I am also currently an intern in Tinkerbox

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In fact, it is my fellow intern and TechLadies' Kate who invited to speak here today

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so I am glad to here

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so now i understand that most of the audience here are beginner level

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Just to get a gauge, how many of you guys have done OOP in python before?

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Okay, I will say that for those who have not done anything

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I hope that by the end of this talk

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we will get to understand more about

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what OOP is about

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'Kay, I would say OOP is like an intermediate level topic

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but it is a very key topic for you to understand

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for you to move on to do more advanced stuff

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so this is why I chose the topic for today

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but also it is a very broad topic

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so i don't know how much I can cover in 20 minutes

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So forgive me if I speak too fast

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Or skip over certain things

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okay

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so

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just a brief idea of what we will be talking about

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We will only be covering, like, nuts and bolts

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of OOP in python

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So language-specified construct syntax

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That sort of thing

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Because I believe for beginners

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this will be what you will be more interested in

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but at the same time, i hope i will be able to talk a little bit about

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what you called Object-oriented design

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principles of writing good codes

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with design principles, basically

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so

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Before I actually go into the actual materials

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I have a confession to make

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The sad truth is, okay maybe not that sad

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but the truth is that I probably enjoy drawing silly things

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more than I like programming so

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as a result, you will see a lot of

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silly drawings

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Probably more silly drawings than code

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in this talk

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but it is my hope that you know

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it will sort of give you a visual aid

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to understanding the concepts

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that I will be talking about

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Okay so

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let's dive right in

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Nuts and bolts

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so these are the topics I will be covering

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Objects Classes & Instances

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Attributes and Methods

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Inheritance and Scope

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And those words have completely

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flown over your head

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Do not fear

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by the end of this talk

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you should, hopefully,

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have a rough idea of what it means

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so

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let's jump straight into the first...

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oh wait, sorry. before that

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i just want to make it clear that

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in common use right now

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there are two main python versions

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so python 2 and python 3

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there are some differences in these 2 versions

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so as beginners

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it can be easy to trip up

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over these differences

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so just to be clear that

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when you read up resources online

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for example, you should know

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what the version

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those resources are talking about

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which python version they are talking about

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so for clarification

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just be clear

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I am using python 3 for all my examples here

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alright

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so objects

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think of objects as a way of

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logically encapsulating your code

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so objects has what we called attributes

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and methods

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so let's look at this doggeh over here

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i like to think of attributes as

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kinda like

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adjectives?

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or properties

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So for example you say

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the dog is white

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or can have a weight of 7 kg

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so these are like the attributes of the dog

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on the other hand

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methods

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they are kinda more like verbs

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a dog can wag tail and bark

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so these are the things

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the dog can do

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these are like

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methods of my dog object

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this is a slightly lame description

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but i hope can bring across

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into the field of what

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I mean by attributes and method

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and in fact, you know

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in python

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you have your variables and your functions

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right?

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so your attributes and methods

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are just your good ol' friends

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your variables and functions

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the only thing is that

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attributes are kind of like variables

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that are associated with a certain object

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and methods are functions

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that are associated with a certain object

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in the end,

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objects basically is a way of calculating data

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and a form of attributes

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with functions of procedures

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in the form of methods

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Okay

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so let's look at this dog transcribe into

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real python code

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for those who have not done any OOP in python before

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this syntax might look intimidating but

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hopefully by the end of it

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you will be able to understand

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what's going on

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The kind of object-oriented programming

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in python

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that we are dealing with

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is called class-based object oriented

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programming

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This is the kind of OOP

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you will find

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in languages like Ruby, Java, C# and etc.

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Only the most popular kind of OOP

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Just so you know,

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there are other kinds out there

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Class-based OOP

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you see here that

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I am defining this class "dog"

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you should know by now

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that in python,

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indentation is intactly(?) significant

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so all these indented code

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this is inside the class body.

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This is my class definition.

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Now I am talking about classes

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Now I have to talk about

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like explain about

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classes and instances

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Because we are talking about class-based OOP

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so what are classes and instances?

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So, think of a class as a kind of category

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where an instance is

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particular living example

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of a kind of thing

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To drive the point across,

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let me talk about babies

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Yes! Babies

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When you think of

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a baby right..

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a human baby

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you kind of have this conception

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tectonic idea of what babies

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should look like

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sweet, tender, angel

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angelic things

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That is sort of like class

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this general category

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this general idea

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whereas if you actually

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see this real living kicking screaming

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pooping baby

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you are like

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"What's this ugly yoda-like thing?"

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That is kind of like instance

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that's the real concrete

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instance of a baby

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So I hope that kinda brings across the idea

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of what's the differences between

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the class and instance

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Let's go back to the code

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and in my class

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so in this class definition right

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when I define my class

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you can think of it as

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defining a custom data type

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so you know in python

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we have our built-in types

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we have integers

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we have strings

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we have lists

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we have dictionaries

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When you define your class

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it is as if you are building

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your own data type

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And this one data type

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has its own attributes and

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its own methods

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I will go through the stuff here later

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but let me go down to the code here

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so what you see down here

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in this line, line 13

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this is where I instantiate

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I create an instance for my class

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So I am assigning

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I am creating

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an instance called "Doggeh"

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And this the way I construct

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my instance

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by calling the, what we called

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the class constructor

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So this is the class name

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the parenthesis

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I pass in certain arguements

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to initialise my instance

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so now I have this Doggeh

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which is an instance of a dog class

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Okay

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so now that we sort of know

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what classes and instances are

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let me go back

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I will start going through the code here

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So to understand the code in here

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we have to talk about

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attributes and methods

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When we talk about attributes and methods

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There are two kinds

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They can be instance attributes or instance methods

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or they can be class attributes and

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class methods

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But for now

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I will talking about instance attributes

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and instance methods

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Because that is what we usually deal with

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Inside this class body

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I define several methods

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for my dog class

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so these are how you define functions

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I mean, methods are just functions

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but they are inside a class

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This is how I define my methods

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And

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you notice that

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this first method looks kind of special

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with the double underscore in front

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So double underscore init double underscore

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so i will be talking more about this later

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but let's look at these two

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func.. methods first

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Now you will notice something interesting

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about this method

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I mean, in the end,

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these methods are just stuff that

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they print something to the console

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right

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It is going to print "Wag Wag" or

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"Woof Woof"

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but there is something interesting about this

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in the method signature

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I am actually taking this parameter 'self'

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and

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this 'self' is actually an indication

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to you that

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these methods are instance methods

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We can invoke these instance methods

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by using this Dog syntax over here

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so I invoke "wag tail" by

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calling it Doggeh.wag_tail()

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And just to emphasize that you have

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to put the parenthesis there

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to invoke the method

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