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Friends, here

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we are going to discuss about loops.

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First of all loops are useful to repeat some blocks, to execute

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a block of code many times. Why we need to execute a block

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of code many times? Block of code is nothing but maybe single

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line or multiple lines.

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But why we need to execute again and again this block of

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code? What is the need, right?

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Let me explain this with the first one simple example.

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Right. See I am going to save a program named called

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'introduction_to_loops.py', and here

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what I am doing is, I am taking some list, suppose assume that I

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have a list of some values. Now here actually, I have a small

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requirement. That requirement is, I need to print the values

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of your list one by one, not at a time all your entire list.

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I mean, I don't want to print your values

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in this way. You are getting output as a list.

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No, I don't want to print in that way.

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I want to print first 4, then 5, then 6. Then what you are doing?

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To get that, first you have to take first value from your

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list. With index

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I am taking first value.

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Then I want to take second value,

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then I want to print it.

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So taking second value is nothing but 'my_list[1]'. Then

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you're printing. Then take third value and then print it.

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[no audio]

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See the output. Yes, you are getting one by one value.

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Okay, for this list suppose you are having three 'print' statements.

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Just assume that in your list

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you have some this many number of values.

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Now, I need to write how many number of 'print' statements?

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How many values you have in your list that many number of

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'print' statements I need to write. So finally, what is the purpose to write

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your 'print' statement that many number of times? Simply you're

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taking one by one value from your list and you're printing

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that. Taking second value, print; third value' fourth value; fifth value

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Likewise, you are taking one by one and your printing it.

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So if you have more number of values in your list, you

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need to write more number of 'print' statements.

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I don't want to write in that way. Because Python is providing,

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not only Python in all languages

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we have this concept.

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Anyway, Python is providing a simple logic.

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Just to take one by one value from your list

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just to take one by one value from your list. How you can

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take one by one value from your list automatically, right?

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See that, as of now for your understanding purpose, directly

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I am writing syntax called 'for each_value in', your list.

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So you can write your variable here or you can also write

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directly your list. Both will be fine. Okay. For time being I am writing

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directly your variable, sorry your values.

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Then after that you have to write ':'. Then 'Enter'.

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First of all, what is your health,

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what is the action of your 'for' here? Means, because of this

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'for', what it will do means, it will take one by one value from your list.

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First it will take 4, number 4, and it will store automatically into

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your variable called 'each' variable. After that, in case if

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you write any number of lines inside of your 'for', these lines

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will execute once.

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Then after execution of this part once, your Python will

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automatically take second value and this value will go and

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store into that. Then whatever the lines you have under

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your 'for', those lines will execute.

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So as of now, my intention is I want to print all the values.

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Right. That's why what I am doing is simply 'print(each_value)'.

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[no audio]

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So guys this 'print' is nothing but, just you are printing your

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'each_value' variable, 'each_value' a variable. In this you have

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some value. And I am writing this 'print' statement under your

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for loop, under your for loop.

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So because of this what will happen means, observe that. Whenever

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if you run your Python script assume that there is no first

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line. As of now assume that there is no first line.

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Okay. Then whenever there is a keyword at very

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first in a given line, Python will immediately go and look

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after 'in'. Whatever

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it is there first

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your Python will observe this.

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Yes, it is a list.

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That's why, in list whatever the value we have, first value,

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that value will automatically store into that.

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[no audio]

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Now very first time your 'each_value', 'each_value' variable is

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number 4, and after taking that whatever the number of

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lines you have inside of your for, those lines will execute

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once. But as of now I'm taking only one line. So while executing

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that line what I am doing? I am printing the variable of

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'each_value', whatever you have.

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in this. So that what you will get? You will get number 4.

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Right. Then after printing, after the execution of this line,

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your Python will automatically take second value, and this

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value will store into this variable. After storing your second

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value into this variable,

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this block will execute once again, but while executing what

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we are doing? This variable value we are printing. That's

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why you're going to get second value. Likewise,

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your Python will take one by one value from here and that

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value will store into this variable

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first. After that only this

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block will execute.

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So because of that see what it is doing.

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You're getting all values one by one after running your code.

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So now, guys actually what you are doing,

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I mean your Python? Taking first value, storing into that, executing

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this block, then taking second value, storing into this variable,

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then executing this block, taking third value, storing

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into this variable, and then executing this block. You're repeating

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here itself, right?

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That's why this is like a loop, and that's why this is called

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loop. And one more thing, executing your block of code, right,

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with the help of your loop, how many number of times? How many

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number of values you have inside of a list, that many number

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of times you are repeating, and each repetition is called

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iteration. Iteration.

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[no audio]

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Right. So suppose assume that in 'my_list'

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I have four values. Just assume that. Then you are going to

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iterate, iterate, this logic, this line, you're going to repeat

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this line 4 number of times, or 4 iterations will

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happen if you have 4 values.

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Not only this, simply your variable, see

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I can also do something like 'print' in this way.

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Just I'm doing this one.

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Let me write three 'print' statements,

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not only 'print' statements, you can write anything.

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But as of now just for our understanding purpose

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I am writing simple lines.

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Now, let me remove this list.

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Okay. Very first line itself our loop.

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I don't want to write this many number of values,

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let me write, suppose three values,

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same action will be repeated for all values, in case if you

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have any number of values. Now what will happen? First thing,

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whenever if you are executing, your Python will look very

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first word, right. If it is 'for' then 'for' is a loop,

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that's why your python will immediately look in the same

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line after 'in' whatever you have,

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your Python will look that place first.

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Then what you are having here? List, which consists of

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three values. Then Python will immediately take first value, and

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this value will store into this variable. After storing that

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the number of lines which you have inside of your loop, those

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lines will execute once. While executing, in case if you want

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to use this variable you can use it, otherwise no problem.

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As of now three 'print' statements. First 'print' statement, simply

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some string you're printing. Second 'print' statement, you are

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printing some variable value. That value is nothing but the value

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which is there currently in this variable. Then after that

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again you are printing this.

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Right. Now, let me write a different symbol

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so that it will be clear for you.

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[no audio]

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Now, let me run it and see the output.

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[no audio]

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First time, second time, third time; you are repeating your

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logic three times.

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This is for first time, this is for second time,

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and this is for third time. While repeating, while executing

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this first time, 'value', this variable is 4, and we are executing

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that. That's why you are getting output as a 4. Now,

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I don't want to use this 'each' variable inside of my loop.

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Yes, no need to use that.

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It's not mandatory. Based on requirement we will use it.

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I am writing simply,

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"This is a iteration". Any message also I can write it.

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[no audio]

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Let me save it and observe the output. I am running.

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While executing first time, three 'print' statements,

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"--This is a iteration", and then some line.

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That is for 'each' value 4. Then second time, 5 value, with

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5 you are repeating this, six you're repeating that,

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that's why you are getting three times.

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So guys here, not only take, I mean you can take any variable.

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Not only 'each_value',

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I can take simply 'x' also. No problem. See the output.

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[no audio]

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That's it. Okay. So this is called simply your for loop.

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So finally you have to understand that this for loop is useful

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to repeat some block of code or some set of lines

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based on your requirement how many times you want to repeat.

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So that is decided by the value which you are providing here.

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Not only list, you can take some other things as well.

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I will show you that. Right. Fine.

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So why loops are useful guys?

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So in all programming languages we have a requirement to

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execute some block of code number of times, many times.

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So that's why we are using loops concepts. Now in Python

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we have two types of loops - for loop and while loop.

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[no audio]

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Okay. Now, for loop. For loop in Python is used to iterate or execute

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many number of times over a sequence. That sequence maybe

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a list or tuple or string or any other iterable objects.

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As of now, don't worry about iterable objects.

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[no audio]

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You are going to repeat some block of code using loop, and

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while repeating, see previously we used somewhere here list,

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right. Not only list,

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you can also provide a list, tuple, or a string.

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Let me show you that.

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[no audio]

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This is using list, right?

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I can also use in your loop a tuple also, no problem.

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[no audio]

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Let me do that now with the help of tuple.

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'for value in', this is a variable guys,

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you can take anything based on your requirement, in your tuple,

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let me write directly my tuple. '(4,5,6', then ', "hi")'.

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Now how many values are there in your tuple?

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Four values. This is a string,

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but this string is one value for your tuple. Four values.

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Right. Now, simply

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I am writing, 'print("hi")', or simply

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I'm writing this "=". Then because of your loop, for loop

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you are repeating this line, you're printing this line,

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you are repeating this line.

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How many values you have? Four values.

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So four times you are going to execute this line again and again

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immediately. Now see the output. Four times you are getting.

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But while executing the block which is there under your loop

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at that time in case if you need a variable value of, 'value'

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you can use it. Now see that. That's it.

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So whether you want to use your variable, whatever you have

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here, that variable you can use it or you can skip it.

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Right. Now, let me give one simple example.

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[no audio]

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Assume that. Yeah, before going to that example

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I will take one more thing, string. As of now

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we worked with list, tuple, then let me take string.

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After that, I will go with one example.

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For, let me take, yeah, 'for each_char in', let me take 'python scripting',

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space is also a string, right, then ':'.

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Then what I am doing is, 'print(each_char)',

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or if you don't want to do that,

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[no audio]

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let me simply do simply "python".

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Okay. Then simply print, I am printing hyphens.

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So now you are going to repeat this line based on how many

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characters are there in a given string.

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So how it is going to repeat means, immediately, whenever if

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you run your Python script, because this is a loop, 'for', your

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Python will take first character from here.

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If it is a list it will take first value from your list, or

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if it is a tuple it will take first value from your tuple.

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But now this is a string, so it will take first character

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automatically and that character it will store into this variable.

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After storing that, whatever the logic, whatever the block,

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whatever the lines you have under your loop, those lines will

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execute once. While executing if you want to

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use this variable you can use it,

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otherwise you can skip it. As of now, I'm not using. Simply

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what I am doing? See the output, you are getting hyphens.

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How many times? Six times, because you have six characters.

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Now what I am doing is, along with your hyphens,

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I'm also going to print the characters which is stored in

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your 'each_char' variable. Now see the result.

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'p-y-t-h-o-n'. See, first time your Python is taking letter 'p', character

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'p', and it is storing into this variable. After storing into this variable,

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this line will execute once, first iteration.

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This is called first iteration. Then because of that you are getting

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'--', and then 'p'. Then Python will immediately go and take next

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character 'y'. Then 'y' is going to store into this variable. After

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that your Python will execute this line once. So while executing

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now you're printing this variable. Currently the value which

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is there in your 'each_char' variable is 'y', that's why

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you're getting 'y'. Likewise it should go to up to 'n'. Right.

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Assume that you just now printed 'n',

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I mean with the help of your loop, after that again your

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Python will try to get next character from your string but

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you don't have anything. All characters are over.

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That's why your Python will come back, come out from your

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loop, and after loop if you have any lines, those lines will execute.

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Right. That's it.

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So guys, 'print' statement,

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I want to repeat. That's why that line should be there under

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this for loop.

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That's why I am providing some space. Suppose

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if I write one more line, 'print()'

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[no audio]

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"we are working with loops". Now see that. This line will execute

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only once. When it is going to execute that one time is after

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complete execution of

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your loop. Because this 'print' statement is outside of your

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loop, there is no relation between this line and your for

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loop. So in case if you have a relation between this for

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loop and this line, this line should be there inside of your

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loop. If you want to write this last line inside of your

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loop, you have to provide some space, and the lines which

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are there under your loop should have same space for each

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and every line. First

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let me run it and see the output.

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[no audio]

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See this last line you're

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getting only once because that is not a part of your

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loop. It is outside of your loop. Only the lines which are

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there under your loop, those lines will execute, right. Now

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I want to write that line also inside of my loop

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then write for all your lines same space,

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right, so that these two lines are there now under your loop.

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Now your loop will repeat these two lines based on how

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many characters you have in your string.

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So six characters, now these two lines are going to repeat

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six times. See that. That's it.

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[no audio]

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Right. Fine.

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Now, let me go with one simple example as of now.

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[no audio]

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Assume that

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I have a list which consists of some values.

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Otherwise, you can also read your list from your command

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line, right. Using your 'eval(input(

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"Enter your list of values: "))'

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you can read it. As of now

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I am taking 'my_list'.

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I don't know what are the values there in 'my_list',

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[no audio]

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okay. Maybe any number of values.

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Now my requirement is,

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[no audio]

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I want to

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print all the values from

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your loop, from your list.

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Okay, first let me print that. 'for each in my_list', then

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let me 'print(each)'.

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[no audio]

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Yes, I'm printing. Now

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I'm able to get one by one value. But before printing I want

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to decide whether it is a even number or odd number. If it

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is even number I want to print your number, then "even". If it

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is odd number, I want to print your number and then "odd". Right.

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So that's why what I am doing is, before printing I am finding

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remainder, remainder with two. So 'each

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%2', and if remainder value, if it is equal to 0,

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I can say that that is an even number.

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Now guys, this 'print' is under your 'if'. Be clear.

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If this condition is satisfied then only I want to print this line,

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that's why I'm writing this line under your 'if' condition.

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So if it is 0 then I want to write '--'. Let me write 'f' string, that's better.

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So whatever the variable you have, " is even". That's it.

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'else', 'else' means remainder is not equal to 0, then I can say

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your number, then

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"is odd". Guys, simple example, but it is useful.

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Why means, I am writing number of lines inside of your loop,

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now all these lines are going to repeat based on how many

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values you have in your list. As of now

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this is a list. It may be a list, or string, or tuple, for time being

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Now run it and see the output. 3 is odd, 4 is even, 34 is even. Yes,

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it's working perfectly. Right. Guys, try to understand this

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loop concept by practicing again

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and again same code. See while writing you have to think what

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we are doing, what is the step

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your loop is performing, right?

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If you are able to think about it, then you can easily understand your loop.

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See in real time loops are very, very important.

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Right. Suppose assume that you are going to write some hundred

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lines of some script.

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So if you are going to write some 100 lines or 200 lines

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of Python script, then definitely you are

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going to use 'if' conditions and loops,

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max. Okay.

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Okay, guys, thank you for watching this video.

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And one more thing guys, we have while loop as well, but this

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we'll discuss later.

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So actually while loop is used to execute a block of statements

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repeatedly until a given condition is satisfied. As of now

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don't go with your while loop,

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just think about loop, for loop.

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Okay. Anyway I will discuss about your while loop later.

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Okay. Thank you. Bye.

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[no audio]