Object Oriented Programming in Python - TechLadies Tech Talks

So, it's

Monty Python Flying Circus

okay actually it is not but just so you know

this is where the python language got its name

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

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

currently in the Computer Science / info systems major

And I am also currently an intern in Tinkerbox

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

so I am glad to here

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

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

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

I hope that by the end of this talk

we will get to understand more about

what OOP is about

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

but it is a very key topic for you to understand

for you to move on to do more advanced stuff

so this is why I chose the topic for today

but also it is a very broad topic

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

So forgive me if I speak too fast

Or skip over certain things

okay

so

just a brief idea of what we will be talking about

We will only be covering, like, nuts and bolts

of OOP in python

So language-specified construct syntax

That sort of thing

Because I believe for beginners

this will be what you will be more interested in

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

what you called Object-oriented design

principles of writing good codes

with design principles, basically

so

Before I actually go into the actual materials

I have a confession to make

The sad truth is, okay maybe not that sad

but the truth is that I probably enjoy drawing silly things

more than I like programming so

as a result, you will see a lot of

silly drawings

Probably more silly drawings than code

in this talk

but it is my hope that you know

it will sort of give you a visual aid

to understanding the concepts

that I will be talking about

Okay so

let's dive right in

Nuts and bolts

so these are the topics I will be covering

Objects Classes & Instances

Attributes and Methods

Inheritance and Scope

And those words have completely

flown over your head

Do not fear

by the end of this talk

you should, hopefully,

have a rough idea of what it means

so

let's jump straight into the first...

oh wait, sorry. before that

i just want to make it clear that

in common use right now

there are two main python versions

so python 2 and python 3

there are some differences in these 2 versions

so as beginners

it can be easy to trip up

over these differences

so just to be clear that

when you read up resources online

for example, you should know

what the version

those resources are talking about

which python version they are talking about

so for clarification

just be clear

I am using python 3 for all my examples here

alright

so objects

think of objects as a way of

logically encapsulating your code

so objects has what we called attributes

and methods

so let's look at this doggeh over here

i like to think of attributes as

kinda like

adjectives?

or properties

So for example you say

the dog is white

or can have a weight of 7 kg

so these are like the attributes of the dog

on the other hand

methods

they are kinda more like verbs

a dog can wag tail and bark

so these are the things

the dog can do

these are like

methods of my dog object

this is a slightly lame description

but i hope can bring across

into the field of what

I mean by attributes and method

and in fact, you know

in python

you have your variables and your functions

right?

so your attributes and methods

are just your good ol' friends

your variables and functions

the only thing is that

attributes are kind of like variables

that are associated with a certain object

and methods are functions

that are associated with a certain object

in the end,

objects basically is a way of calculating data

and a form of attributes

with functions of procedures

in the form of methods

Okay

so let's look at this dog transcribe into

real python code

for those who have not done any OOP in python before

this syntax might look intimidating but

hopefully by the end of it

you will be able to understand

what's going on

The kind of object-oriented programming

in python

that we are dealing with

is called class-based object oriented

programming

This is the kind of OOP

you will find

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

Only the most popular kind of OOP

Just so you know,

there are other kinds out there

Class-based OOP

you see here that

I am defining this class "dog"

you should know by now

that in python,

indentation is intactly(?) significant

so all these indented code

this is inside the class body.

This is my class definition.

Now I am talking about classes

Now I have to talk about

like explain about

classes and instances

Because we are talking about class-based OOP

so what are classes and instances?

So, think of a class as a kind of category

where an instance is

particular living example

of a kind of thing

To drive the point across,

let me talk about babies

Yes! Babies

When you think of

a baby right..

a human baby

you kind of have this conception

tectonic idea of what babies

should look like

sweet, tender, angel

angelic things

That is sort of like class

this general category

this general idea

whereas if you actually

see this real living kicking screaming

pooping baby

you are like

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

That is kind of like instance

that's the real concrete

instance of a baby

So I hope that kinda brings across the idea

of what's the differences between

the class and instance

Let's go back to the code

and in my class

so in this class definition right

when I define my class

you can think of it as

defining a custom data type

so you know in python

we have our built-in types

we have integers

we have strings

we have lists

we have dictionaries

When you define your class

it is as if you are building

your own data type

And this one data type

has its own attributes and

its own methods

I will go through the stuff here later

but let me go down to the code here

so what you see down here

in this line, line 13

this is where I instantiate

I create an instance for my class

So I am assigning

I am creating

an instance called "Doggeh"

And this the way I construct

my instance

by calling the, what we called

the class constructor

So this is the class name

the parenthesis

I pass in certain arguements

to initialise my instance

so now I have this Doggeh

which is an instance of a dog class

Okay

so now that we sort of know

what classes and instances are

let me go back

I will start going through the code here

So to understand the code in here

we have to talk about

attributes and methods

When we talk about attributes and methods

There are two kinds

They can be instance attributes or instance methods

or they can be class attributes and

class methods

But for now

I will talking about instance attributes

and instance methods

Because that is what we usually deal with

Inside this class body

I define several methods

for my dog class

so these are how you define functions

I mean, methods are just functions

but they are inside a class

This is how I define my methods

And

you notice that

this first method looks kind of special

with the double underscore in front

So double underscore init double underscore

so i will be talking more about this later

but let's look at these two

func.. methods first

Now you will notice something interesting

about this method

I mean, in the end,

these methods are just stuff that

they print something to the console

right

It is going to print "Wag Wag" or

"Woof Woof"

but there is something interesting about this

in the method signature

I am actually taking this parameter 'self'

and

this 'self' is actually an indication

to you that

these methods are instance methods

We can invoke these instance methods

by using this Dog syntax over here

so I invoke "wag tail" by

calling it Doggeh.wag_tail()

And just to emphasize that you have

to put the parenthesis there

to invoke the method