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[no audio]

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Friends here we are discussing about

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inheritance and polymorphism concept

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of OOPS. First

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let me go with polymorphism.

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See basically we know 'poly' means many.

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So in Python polymorphism allows us to define same methods

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in different classes.

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I mean, you can take same method name in different classes.

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Even though if you define same method name in different classes,

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there is no overlap, and this process is also known as method

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overriding. Simply we are overwriting same method in

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different classes. Yes, that is possible, that is allowed in

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your Python. And we can also use this polymorphism concept in your

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inheritance as well.

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We will see that while discussing about inheritance. First

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let me explain about your polymorphism with a simple

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simple example. Let me open my Sublime Text Editor.

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So here I am defining two classes,

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let's say 'tomcat',

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[no audio]

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and I am defining a constructor method here.

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The purpose of constructor method is to assign, let's say

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'tomcat', 'home' and 'version' by default whenever we are creating

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an object. We know initialization method is a constructor method.

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It will execute by default whenever if you create an object.

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Right. So simply I am writing 'home',

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then let's say 'self.version = ver'.

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Right. Then finally write,

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I'm not expecting any 'return' value from this method,

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that's why simply I am writing 'return None'. Then let me write

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one more method called 'display'.

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[no audio]

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So simply I am writing,

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"This is from tomcat class", and here

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simply I am displaying 'print(

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self.home), then 'print(

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self.version)'.

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That's it.

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Then from this function

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also, I mean from this method also I'm not expecting any

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return value. Simply I'm writing 'return None'.

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Let me take same method.

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[no audio]

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But here I am taking web server class name,

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let's say 'Apache'.

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[no audio]

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Yes, we created two classes.

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But if you observe, here I have taken initialization method,

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and here also I have taken initialization method. 'display' method

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common in both the classes.

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No problem. It is allowed in your Python.

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It is allowed in your Python.

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[no audio]

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Right. See if I run this code you're not getting any error.

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Anyway, let me create an object from your 'tomcat',

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and from your 'Apache'. Let's say 'tom_ob

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= Tomcat()'.

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So while creating an object you're having initialization

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method which is expecting two arguments,

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let's say 'home' and 'version'. Then let me pass that. Lets say

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'/home/tomcat.

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[no audio]

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9', and then I am taking suppose 'version' as some 7.6,

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something like that.

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Then let me create 'apa_ob' also

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from your 'Apache' class.

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So it is also using initialization method, that means it is

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expecting two arguments,

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we need to pass them while creating an object.

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Let's say 'version' as some 2.4. Let me run this and see the

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result. There is no error.

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That's fine.

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Now I want to display the details of 'tom_ob', and also

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display the details of 'apa_ob'. Now in 'tom_ob'

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we have 'display' method. If I call this 'display' method

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with respect to 'tom_ob'

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then it will call from here only so that you are going

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to get information for your tomcat object. See guys

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simply we define same method name in different classes. No

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problem. Even though if we take your Python don't get confused,

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it will work perfectly. See the result.

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[no audio]

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This is from 'Tomcat' class.

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[no audio]

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Right.

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Let me call from 'apa_ob', 'display' method.

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Now what you are going to get, see the result. "This is from"

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Yeah, sorry. I have written, actually I copied, right,

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let me modify here 'apache'. Both the places

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actually we have same code. Now,

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let me run this and see the result.

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Whenever if you are calling

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from 'tom_ob', 'display' method it is going to execute your

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this 'display' method, right. And whenever if you're calling

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from 'apa_ob' it is executing the method which

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is there in 'apa_ob'. That's it.

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Even though if you override your method in different classes,

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your Python won't get confused, and this is simply polymorphism.

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Defining same method name in different classes is nothing

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but polymorphism, right?

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That's fine. Now our next concept is inheritance.

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See inheritance is a mechanism that allows us to create new

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class known as a child class, and that is based upon an existing

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class. That is parent class.

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Nothing is there. This concept is very similar to our

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[no audio]

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like human life. Suppose

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we are inheriting genes from our parents.

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Right. That is the concept here.

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Let me explain this with a script so that you can understand.

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Now, let me take one more script.

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So here I am saving it as a 'inheritance.py'.

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[no audio]

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So guys first thing let me take same script only,

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[no audio]

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and if I open this script here.

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Guys, if you observe in these two classes, there are common

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methods, at least 'display' method.

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[no audio]

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See, for 'display' method already it is there in 'Tomcat'.

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Why should I write a code here? If you observe entire syntax

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is same no, here and here. If it is similar

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why should I write same code in the second class?

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[no audio]

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Right. So in that case, what I can do is I can inherit 'Tomcat' class

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in my 'Apache' so that I can use 'display' method for 'apa_ob',

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for 'Apache' class. How it is possible? Just observe

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that. I am removing 'display' method from your second class.

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[no audio]

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And if you want to inherit any class, instead of this object

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you have to write the particular

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class name. That's it.

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Now the meaning for this is, you are inheriting these two

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methods in this class.

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And if you observe same method is there here and here. No

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problem. Even though if you are having, first preference is

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in this Apache, this one. If it is not there in Apache, then

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only it will take this initialization method. That is called

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polymorphism. That's fine.

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Now see, let me create your two objects.

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[no audio]

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Right. Now remove this 'print' because you are inheriting this

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'Tomcat' into this 'Apache' class.

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Now, I created two objects.

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It's fine. There is no error. Right. Now

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see I am calling your 'tom_ob.display'.

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[no audio]

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Then you are getting 'Tomcat' details.

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If you observe in 'Apache' we don't have, we don't have 'display'

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method, but I am trying to do that. 'apa_ob.display'.

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[no audio]

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You're getting your information. Your 'display' method is executing

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even though if you don't have 'display' method here because

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we inherited this 'Tomcat' class into 'Apache', so that whatever

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the methods are there in this 'Tomcat', all methods are valid

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in this 'apa_ob' also. But initialization method is

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already there here and here, that's why preference is for this

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initialization method, not for this.

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[no audio]

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Right. So this is the way how we can inherit a method of one class

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into other class. What we are doing? Simply while creating

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your second class

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we are writing in place of parentheses, in place of object

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we are writing your required class from which you need to

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inherit, from which you need to import the methods, that class

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name you have to write so that the methods which are available

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in your this class will be available with this object

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also, I mean, whatever the object you are going to create

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from this class also. That's it.

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That is the simple way to understand inheritance concept.

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Anyway, you will get more ideas while writing our real-time scripts.

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Okay. So finally, what is the advantage by using inheritance? Simple.

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This saves you from duplicating a lot of code. Suppose

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you are defining same method in different classes and with the

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same code. Why should we repeat same code in different classes?

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Define in one class and inherit that class into your current

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class, so that you can use the previous class methods in the

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current class also. That is the advantage. And one more thing.

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Yeah, last point.

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[no audio]

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For 'Apache', we are inheriting methods from 'Tomcat'. Now, here I

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can say 'Tomcat' is the parent class and 'Apache' is the child class,

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or 'Tomcat' is the superclass and 'Apache' is the subclass.

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You need to remember those names.

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Parent, 'Tomcat' or superclass is 'Tomcat'. 'Apache' is the child

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class or subclass.

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Right. That's it guys.

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Thank you for watching this simple video.

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[no audio]