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Welcome back, everyone, to part three of our continued discussion, object oriented programming.

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We're going to discuss methods.

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Let's head back to our code editor.

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All right.

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So here I am inside Visual Studio Code Editor Now, when we're talking about methods, they're really

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just functions defined inside the body of a class, and they are used to perform operations with the

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attributes of our objects.

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Now let's go ahead and create a class called Circle.

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So we have our instance of a circle class.

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And then for most classes, we're going to be creating an instantiation method or in its call.

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So double underscores, remember, and this is going to take in self and what are the attributes associated

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with a circle?

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Well, one of the attributes can be the radius, so we can have a user define the radius of a circle.

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So I can say radius and then pass in, oops, forgot the colon.

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There we go.

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Say self.

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The radius is equal to the radius passed in by the user.

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Now, if you want a default value for your radius, you can always say something like radius equal to

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one, and that will set a default value to one against the actual user doesn't define radius upon creating

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a circle.

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So now outside of this, I can say my circle is equal to an instance of circle, and if I wanted to,

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I could say something like radius.

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Equal to 20, for example.

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And then I could print out my circle and print out its specific radius, so it's going to run this just

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to check if it works.

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And now I see the output of 20, so I have this very simple circle class and then in order to create

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a circle, I do need to define its radius.

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Otherwise, we'll have a default radius of one.

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If we think back to class object attributes things that are true for any instance of the class, such

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as Circle, I could say that PI is a class object attribute, so I could say PI is equal to three point

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one for save that change.

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And so three point four makes sense to be a class object attribute because regardless of the radius

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of the circle, it should always have the same PI attribute.

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Three point one For now, let's talk about adding in more methods.

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This init method is technically a method within the actual circle class, but now we want to expand

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on things that are circle class can do.

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For example, let's imagine I wanted to calculate the area of a circle.

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I could create a method for that, so I could say something like the F area.

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And then to make it clear that I'm going to be performing this method using attributes from the instance

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of the class I pass in self here that essentially connects this function to be a method operating on

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the class.

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And here I can decide whether I want to print or return.

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Typically, methods are going to return in the same way functions usually a return they don't usually

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print.

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So to calculate the area of a circle, it's going to be its radius squared times PI.

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So I'm going to say return self-taught radius.

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Notice how I say self dot radius because I'm passing in self, which now allows me to have access to

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self, but radius up here.

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I can't just say radius by itself because I was only passed in in the in its method.

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It's not actually being passed tense area, which is why I say self, but radius.

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Now remember it's self that radius squared.

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So I could say times self radius and it's pi are square.

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So I do need to multiply it by PI.

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There's two ways I could do this because PI is a class object attribute.

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I actually have the ability to say circle that PI and I can do this circle that pi.

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There we go.

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I can do this for class object attributes because PI doesn't change regardless of the instance of the

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circle or what I can also do is, say, self-taught pi either is OK.

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Circle that PI basically shows somebody who's reading that method that, by the way, PI is a class

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object attribute, but either of these methods should work just fine.

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So no, again what this area method does, it takes its self and then it can use attributes in order

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to return something.

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So I'm going to define a circle with a radius of four.

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And then I'm going to call area and notice how I'm not actually passing in open and close parentheses

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into area.

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We'll see why in just a second.

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In fact, we should be calling parentheses, but I want to show you what happens when you don't.

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If I just run it like this, it says, Hey, this is a bound method, circled the area of this particular

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circle object at this point in your computer's memory, this area.

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Notice how it's not actually inside in it.

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In fact, area, just like a function, needs to be executed with open close parentheses.

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If you just say my circle dot area, that's not actually executing this function slash method.

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Instead, what it's doing is just reporting back to you.

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Hey, area is this bound method for a circle object created at this point in memory to actually execute?

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Area, I need to open close parentheses on it.

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Now, when I run this, I see that the area of the circle of Radius four is equal to fifty point two

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four.

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Let's go ahead and try to finding another method.

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Let's make this method for perimeter.

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In fact, try to pause the video and see if you can do this yourself.

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So how do we define perimeter?

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Well, we're going to say is create another method called perimeter.

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Again, it takes itself that way.

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I can access those attributes.

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And then I'm going to return the perimeter, which is just two times the radius, times PI.

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So I should be returning to.

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Times the radius, self-taught radius.

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Times softball pie, or if it's a class object attribute, you could also say circle that pie.

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It's up to you when you want to use.

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So let's now instead of calling area called the perimeter.

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Save that change.

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Go ahead and run this now I can see the perimeter being reported back and again, this can be circled

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that pie, or it could also be soft that pie.

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Now you may be wondering which one's better to use circled up higher self the pie.

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Some people sometimes they prefer to use circle because it lets someone know as they're reading this

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method.

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Oh, by the way, circle that pie.

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That's a class object attribute not defined by the user.

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Other people like the consistency of just having everything self.

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Either way, it's going to work the same, so I wouldn't worry about it too much for our use cases.

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In fact, we're not going to see too many class object attributes as we continue to work with our own

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object oriented programming creation within the context of Django.

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All right.

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So let's again review our methods.

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We have this init method, which we have for most of our instances for classes and then we can define

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our own methods.

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These are really simple methods that I did all on one line.

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But keep in mind, I could create new variables here, so I could say something like, Hey, inside

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of this area.

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Go ahead and do something like results is equal to self thought radius squared, and then maybe I want

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to update results within results as equal to results times self-taught pi.

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And then here return.

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Result after it got updated, so this is the same thing, it's pi times our squared and here I'm just

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returning the result.

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But just keep in mind, I'm now able to use these variables that I want within the context of this method.

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Note that I don't need to say self here because this is a little temporary variable that only lives

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within the scope of the area method when we're talking about things like self.

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Those are attributes of the object that can be accessed as long as we say self inside the actual method

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of call, which by convention we typically always do.

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All right.

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So those are the way method works.

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You can think of them as just functions that you're defining inside of the class that can then access

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attributes of the class in order to perform some sort of calculation.

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And keep in mind, you can also make method calls that update the actual attributes themselves.

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It's not as common as grabbing the attribute, but you could go ahead and do something like that.

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So I'm going to create kind of a silly method here, and this silly method is going to be called double

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radius.

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And then takes in self.

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And what this methods actually going to do is what it says.

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It's going to take the existing radius and then double it.

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So it's going to say self that radius is equal to so that radius times to note what's happening here.

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I'm saying grab the current radius, multiply it by two and then reset the existing radius to that.

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Keep in mind, this method doesn't really make sense to return anything, I could maybe print out a

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result saying something like radius has been.

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Doubled to.

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And maybe use f string literal formatting here, that may be something I want to see reported back up

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to user and then I would simply say self-taught radius here.

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This is just to give you the idea that the methods themselves can permanently change the attribute values.

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So let's go ahead and check this out.

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I'll create a circle for radius of four and then instead of calling perimeter, I'm going to say.

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Double the radius and here, I don't need to actually print anything up because nothing's being returned.

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So I'm calling my circle double radius, which should I expect to grab the current radius and reset

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it to the double of it?

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Then it's going to report back that the radius has been doubled, although keep in mind, it doesn't

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actually return anything, it's just printing out the report.

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This is just to show you that methods can effectively update within attributes, and they can also take

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in arguments and then do whatever they want to the current existing object.

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So I go ahead and run this and it says, Hey, radius has been doubled to eight.

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In fact, let's go ahead and prove it to ourselves by saying print.

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My circle, that radius, which I should also see, is now eight after I had initially defined that.

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As for?

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And there it is, Radius has been doubled to eight.

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And so when they print out that radius, it has been indeed updated to be eight methods.

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It should also be pointed out, can take their own parameters.

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So now this is going to be called multiply.

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Radius, and now I'm going to take in a parameter to multiply by, so some numbers multiply.

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And so instead of saying self-built radius times two, I'll say.

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Self-taught radius times the number, and then I'll say radius has been changed to the updated now self-taught

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radius.

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So instead of calling double radius here, I'll say multiply radius.

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Now keep in mind, multiply radius as visual studio codes telling us requires some number to be passed

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in.

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Let's see what happens.

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If I don't pass in that number, I should expect an error.

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And there's the error.

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It says, Hey, multiply radius is missing that require two positional argument number, so I can pass

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that in.

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Let's say 20.

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I run this an hour radius has been changed to 80, and I can see the uptick here four times 20 is 80.

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That's just to give you the idea that methods can accept their own arguments and then use those arguments

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inside.

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You should also note how this particular argument not being within in it did not require something like

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soft, but no, because I'm only using this number at the scope of multiplied radius.

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I'm going to permanently affect the attribute radius, but I don't need to bother, say this particular

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number as some sort of attribute of the circle object because it's just a number that the user happened

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to pass in.

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OK, that's it for simple methods.

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Coming up next, we'll talk about inheritance.