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Friends, we know that loops are useful to repeat or iterate

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a logic and already we have seen for loop.

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Now we have one more loop with your Python that is called while loop.

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Let me explain about your while loop by taking simple example.

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First of all, I am taking simply 'print(

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("welcome to loops")'.

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Suppose I want to print this message only one time, then I can

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directly write 'print ("Welcome to loops")'.

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But I want to print this message 10 times, then what I can do?

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One thing is, I can write this statement 10 times,

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'print ("Welcome to loops")',

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"Welcome to loops", likewise, 10 times I can write. But already

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we know for loop, that's why what I am doing is, I am going

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to iterate. I am going to iterate this logic for 10 times

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'for each in range(10)'.

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Not only 'range(10)', directly you can provide a string which

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consists of 10 characters, such that once if you run your code

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it is going to repeat your, it is going to print your message 10 times

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But I want to print this message infinite number of times.

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[no audio]

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I want to repeat this message for infinite number of times.

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Let me modify this for loop with, 'while True'. Now see the

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result. So to get more clarity

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I'm writing one more line here so that you can understand

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whether it is going to repeat it infinite number of times or

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not. See that.

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It is going to repeat for infinite number of times.

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Right. So sometimes you may need to repeat your logic for infinite

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number of times.

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Let me give you a very simple example. First let me stop it.

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So if you write 'False', then it will stop.

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[no audio]

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That's fine. So first of all, you have to understand that if you want

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to repeat a logic for infinite number of times, then you

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have to go with while loop.

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Right. So guys how it is going

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to work? Yeah, let me explain that as well.

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[no audio]

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See whenever if you run your script with this while loop,

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because of while, right, while is a loop,

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first of all, this logic will repeat. But how many number of times?

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If you write directly 'True' here, then it is going to repeat

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for infinite number of times.

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Same logic will re-execute for infinite number of times

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if you write 'True'. How it is doing means, whenever there

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is a while, your Python will check first the value here.

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It is a True, right, if it is True

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it will execute once. Then again, your Python will come back

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to this position and again, it will check.

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Anyway, this is a fixed value 'True', that's why again it will execute.

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Again our Python will come back to here,

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again this is 'True'. It will execute.

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Likewise it is 'True' for lifetime

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so it is going to repeat for infinite number of times.

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That's why this is a infinite loop. Right.

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[no audio]

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That's fine. Now,

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[no audio]

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what is the use of infinite loop? Let us assume that you

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need to monitor a file system for lifetime.

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Then what I will do is, simply 'True'. Here,

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I will write the logic to monitor your file system. As of

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now, simply I am writing 'print' statement, "Monitoring

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[no audio]

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file system usage",

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just for our clarity

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I'm writing one more line.

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[no audio]

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Now see that,

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for every 1 minute, I need to monitor my file system usage,

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but for lifetime. Then what I will do? Just I'm importing 'time' module.

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[no audio]

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Then after every 1 minute, right, but instead of

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one minute, what I will do is, as of now I am taking simply

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one second. Now for every one second now our script will

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monitor your file system usage. In case if it has reached the

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threshold value, then you can send mail alerts, right. Now see that.

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Once if you run your script and if you leave it, it is going

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to monitor your file system for lifetime. That's it.

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So this is one of the usage, when you want to repeat your

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logic for infinite number of times, right? That's fine.

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Now sometimes you don't know how many number of times you

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need to repeat your logic, but after a certain number of

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times you need to stop.

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Means just assume that

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[no audio]

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I want to print a number then next

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time I want to print your number by adding some random number.

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I mean first let me write logic so that you can understand.

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Let me take initially a 'value'.

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let's say some number 4. Then I am taking 'while True'.

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Then I am printing your 'value', initial value. Then what is

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the next value you want to print? I am taking next 'value +',

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some random number I am adding.

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Now if I run this, see that it is going to get

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some numbers. Right.

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Let me stop it.

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[no audio]

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So in this way if you run, you are going to get your numbers

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infinite number of times,

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I mean infinite numbers you are going to get. Initially 4, then

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460, then 4 something, 900 something, like that you are

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going to get. But I want to, I don't want to get all the numbers.

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I want to get the numbers only suppose

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let me write, if your value

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is less than or equal to some, this number.

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[no audio]

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So here what I am writing,

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I am writing a condition such that, previously here you have 'True', right?

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[no audio]

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So now let me write 'True' first.

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[no audio]

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You're going to get some numbers, but I don't want to get

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all these numbers.

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I want to stop this loop once if I reach my value more

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than this. Now see the result. In case if your 'value' is

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greater than

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6789, then you are going to stop it.

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Actually, I'm repeating this for infinite number of times, but

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I don't want to repeat infinite number of times.

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I want to get the numbers which are less than this.

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[no audio]

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So intentionally you can stop your while loop based on condition as well.

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[no audio]

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Right. Initially this is the value.

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I am printing that value. For my 'value'

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I'm adding something and I am then printing, right.

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Now to get more clarity, let me take simply

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[no audio]

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'while True', simply print("hello").

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Now it is going to repeat infinite

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number of times, but I don't want to print infinite number of times.

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Right. I want to print only for suppose four times.

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Let me take initially 'cnt=0'.

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Now what I am writing is, here I am writing 'cnt' value

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if it is

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'<=', '<5',

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[no audio]

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or you can take even maybe '<= 5'.

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Let me take initially 'cnt = 1'.

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[no audio]

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Right. Now what I am doing is I am increasing count value as well.

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[no audio]

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Now see that you're going to get your output only four five

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times, you are going to repeat this logic only for five times.

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Then how it is working? Nothing

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is there. Simply first you are initializing some condition.

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Sorry, I'm sorry some variable, initializing, 'cnt = 1'.

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So while, first of all while means, you have to assume that

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the lines which are there under your while loop will repeat

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for infinite number of times, right?

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So how it is going to work?

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We know that. 'while' first Python will check this condition

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result, 'cnt' is initially 1, right. 1 less than equals to 5

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means 'True'. If it is 'True',

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your Python will execute these two lines once.

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So because of this you're also increasing your 'cnt' value.

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Initially it is 1, now after executing first time, for first

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iteration your 'cnt' value is becoming 1 + 1, w. Now with

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this 2, now 'cnt' is 2 not 1. Your Python is coming

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to this position, and is checking this condition, 2 less than

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or equal to 5, yes, 'True'.

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Then again it will execute this logic. But while executing this

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logic now you're making your 'cnt'
value from 2 to 2 + 1 = 3.

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Then with this 3 your Python will come to here and 3 less

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than equals to 5, yes, 'True'. Then it will execute once again.

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Now your 'cnt' becomes 4, 3 + 1 = 4.

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Then again, your Python will come to here with it, 'cnt' equals

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to 4, 4 less than or equal to 5, 'True'. Then it will execute

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once again this logic. Now 'cnt' value 5. With this 5 again

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your Python will come to this position, 5 less than or equal

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to 5, 'True'. 'True' means, again this logic will execute once.

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But now 5 + 1 = 6, and 6 less than or equals to 5? No, 'False'.

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If it is 'False', now your Python is going to stop your while loop. That's it.

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[no audio]

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Right. So here we are fixing how many times you want to repeat.

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[no audio]

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Right. Not only that, see based on other condition,

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while adding some number for your initial value, you are

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going to get your value more than this

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after certain number of times.

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You don't know how many times you want to repeat,

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but you know the condition. Once our value is more than this

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then I want to stop it. So here guys, be clear.

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We don't know how many times you are going, after how many

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times you are going to get this number we don't know.

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But you know that certainly, definitely after certain number of times

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your number will be more than this. At that situation

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you want to stop it,

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Right. So while loop in Python is used to repeat or iterate over

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a block of code, as long as the test expression or condition

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is true, right?

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So that's what we are doing here.

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As long as the condition result is true

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then it is going to execute this line. That is one case. Second

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one is, we use this loop when we don't know beforehand the

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number of times to iterate.

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That's what with this example. Really

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we don't know after how many times you're going to get this,

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I mean after how many iterations you are going to get your

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number more than this, we don't know.

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But we know that because of this calculation somewhere,

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somewhere you'll reach your number more than this, at that time

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I want to stop it.

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So that is logic of while loop.

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Right. So guys, be clear.

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One thing is to repeat your logic for infinite number of times.

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Second thing is to repeat your logic until the condition is true.

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And one more thing is, that is the important one, before starting

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your logic you don't know how many times you want to iterate your logic,

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but based on some condition you can stop it.

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So that condition you can use it in your while loop, okay.

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Okay guys, thank you for watching this video. While going

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forward we will see real-time use case of your while loop

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with many examples, okay.

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[no audio]