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Okay, let's take a look at a real life Object Oriented Programming

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example. So up until this point, we've learned about classes,

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class attributes, class methods, and sort of the 'self' keyword,

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and all sorts of stuff behind the scenes there.

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But we actually haven't used any real example.

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So let's use an example where, let's say maybe we have a service

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where we are working with people's pets.

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And so we have different types of animals here.

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So we can say 'class Animal'.

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And in here we can use '__init__', the magic method

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'__init__', always takes 'self'.

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And what 'type' of animal is it?

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What is the animal's 'name'?

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And instead of 'type', because that is actually a word, let's

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use 'species'. Let's ask for a 'name'.

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And I don't know, let's give it a 'weight'.

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And so we can say 'self.species

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= species', 'self.name = name',

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and 'self.weight = weight'.

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Then because every animal can speak, it's going to say something, so

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'def speak(self)',

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and because I don't know what this animal is, it's just going

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to print a grunting sound.

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I guess. Most animals know how to grunt, right?

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And so let's save that.

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And let's create a new animal here.

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So I have an animal.

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His name is "zephyr".

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He's going to be a new 'Animal()' class.

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He is a house "Cat", his name is "Zephyr", and his weight is

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"14.5 lbs".

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He is a larger cat.

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I also have another cat.

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His name is Henry animal cat.

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His name is "Henry", and he's a little bit smaller.

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He is "9 lbs".

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So what we've done here is, we've written a template for an

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'Animal' that's always going to have a 'species', a 'name', and a 'weight'.

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And without having to rewrite 'species', 'name', and 'weight'

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every single time, we wrote out this template, and then we

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instantiated a new 'Animal' class, and we specified

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the 'species', 'name' and 'weight'.

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And the logic that happens behind the scenes is already done for us.

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So at any point in time, I can say, 'zephyr.speak()',

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I can also say 'henry.speak()',

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[no audio]

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and so with just one line of code for each one of these,

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I have now effectively used nine lines of code behind the

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scenes. Now, if you're still not convinced on why Object

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Oriented Programming is useful, without it we would have to

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do one of two methods.

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The first method is really gross.

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It uses a lot of variables.

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So 'zephyr_name = "Zephyr"'.

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'zephyr_species = "Cat"'.

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'zephyr_weight = "14.5 lbs"'.

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Okay, not bad, not bad,

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but now I also need to specify "henry".

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So, 'henry_name = "Henry"'.

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'henry_species =',

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like you get the point here, I'd have to write this out for

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every single animal.

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Now, the thing is down the road is, what if I wanted to get

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Zephyr's weight?

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But let's say this was accidentally not set.

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How do I get his weight?

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Well, I have to check to see if that variable even exists,

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and then if that variable does exist, it is very specifically

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just Zephyr.

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It's not Henry, it's not anyone else.

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This variable is literally just for Zephyr.

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So the reusability of this variable is a lot lower than if

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we used it in a class.

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[no audio]

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The second option is, we can say 'zephyr' is an object or not an

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object, but a dictionary.

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And then we could say 'name': "Zephyr",

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'species': "Cat".

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'weight': "14.5 lbs".

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Now, this is actually not a terrible way of doing things.

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However, if I wanted to also do the same thing about "Henry",

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I would have to copy this over and change his name to "Henry",

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which, again, not a terrible thing, but copy and paste can

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be dangerous because we tend to forget things.

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So he's "9 lbs".

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We can set that as well.

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So that's a little bit easier.

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But let's say you have Zephyr, Henry, Ted, Ezra, and maybe

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like a pet lizard or something.

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And you have to do this for every single pet.

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Well, what if down the road you were changing 'weight' from

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pounds to kilograms, you would have to find every single

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instance of every single animal, which means you have to

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manually scan your code because there's only one reference

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to 'zephyr' here,

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there's only one reference to 'henry' here, well, there's two,

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but in a variable name, there's only the one reference.

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Or if you use the class, you could add some logic in here.

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And you could say 'if weight.endswith("lbs"): "#Convert to

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kilograms". And then you could say 'self.weight =

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whatever the weight is going to be in kilos.

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And now you've effectively updated all of your code.

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So even if someone puts in "14.5 lbs", it's going to say

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it ends with "lbs",

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and it's going to convert that weight to kilograms.

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And not only do you only have to do it in the one place,

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you no longer need to do a search and find for 'zephyr', 'henry',

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'ted', 'ezra', your pet lizard.

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You don't have to do it for every single one.

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And in the variable example, you don't have to go ahead and

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change this from "14.5 lbs" to "14.5 kilos" or kilograms, and

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do the math behind it, because your program will do that for you.

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That is a very, very good reason and a good real life example

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of why we would want to use Object Oriented Programming.

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It is a nice template for repeatable code.

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[no audio]