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So most of you probably know some programming language already.

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And in every programming, language loops are very important and also they are often combined with if

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statements so loops and if statements in Python are very similar to the cases in other programming languages.

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So let me show you here two examples for loops.

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The while loop and the for loop.

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And then we will also combine one of the loops with an if statement.

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So let me get started with a mile loop.

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So the syntax for a while loop is, of course, we start with while and then we have to define some

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condition.

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For example, we could say we have an index called I add this I should be smaller or equal to the number

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of 10, and then we add this to dots and this will start to loop.

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Now, when we press, enter the editor or the text editor here.

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Just you put a notebook in the browser already makes a tab here.

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And this is quite common for Python.

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So you do not write your commands here, but you make a tab so that it works fine.

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So here we have to define what will happen, actually.

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And since our condition will be that the number I must be smaller, equal to 10, we should do something

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with AI.

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First of all, we should define the number AI and we should do this outside of the loop.

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So we should say the starting role, if I could, for example, be one.

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And then in the loop, we increase the value of AI by one every time it loops.

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We increase the value by one.

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So I run this now.

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Nothing happens.

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But also there is no error because we start from April one and then we loop make it two, three, four

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five and so on.

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And then once we are at 11, the wire condition is no longer true.

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So the loop stops and the cell finishes the calculation.

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So what we can do instead is we can add another calculation here or another command.

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And I want to add it actually before I increase the index and I want to say it, just print the number

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I.

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So if I run this now, you see it loops 10 times, increase the value of AI and prints the value of

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AI.

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And then once I is 11, it stops.

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So this is a way to print the value.

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Of course, we could also do something like this.

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So then it gives us twice the value of ESD output.

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So what else can we do with while loops?

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Well, of course, we can add some if statements, and I want to show you here that I want to basically

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copy this.

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And what I want to do is I want to print the value of AI only when it's an even number and when it's

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an odd number.

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Instead, I want to print the word order.

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So how can we do this?

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Well, the beginning is quite good.

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We start from one, we increase the value and we stop ones is larger than ten.

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So the only thing that we have to change is this one here.

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And I do the following I write an if statement, which begins with if so, then here we have to write

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our condition, which I will do in a second.

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Then we will write this again.

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And you see it adds another tab.

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And here we write our command that we want to do or execute when the condition is true.

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So this would be print out and then we go one tap a back so that we are just at the level of if I will

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then write ours and if it's not true, then we we will print the words out.

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And then since this is once again at the same level as if and else this is outside of the if statement

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and this will be done every time.

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So the only thing that we have to now specify is the condition and the condition will be that AI is

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an even number.

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So how can we do this?

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Well, we can calculate the modulus, which I have explained to you at the very beginning.

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So we write like this.

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So this means the modulus of AI and two.

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So basically, the remainder of the divisions, I divide it by two and then you just take the remainder.

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If this is equal to zero, then it means it's an even number.

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For example, if I is eight, then eight divided by two is four with no remainder.

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So this is true.

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So it will print the value eight.

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If it's seven, then seven divided by two is three with a remainder of one.

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So this is false.

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So it goes to Alt's and prints OT.

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So if I run this, you see for every odd number.

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Just Prince, T-Bird, odd and even number it prints to value itself.

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So pretty easy, I think, and pretty much the same as in every other programming language.

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So the for loop is also, of course, pretty similar.

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So here's the only thing or the nice thing where it is useful could be to work with lists so you could

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write for and you have some value, some variables, some running index, for example.

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So we could say for AI in and then we can add here a list.

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So just some random list numbers.

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So this means that we have a running index AI, which takes every well, you off this list and then

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the first loop, it takes this value and the second loop it takes this value and so on.

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And then the fourth one, this one and then sends the list ends.

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Also, the loop ends.

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So this means now we can write what should happen with AI, given the fact that it changes the value

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every time it runs through the loop.

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And of course, the easy thing would be to just print the value of AI.

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So this would give us these four values, of course.

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And what I found pretty cool is that the same thing happens or works not only with lists, but also

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with strings.

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For example, I write for AI in the world, one in the string test print.

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I think you see the result will be all the letters.

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So basically, it treats the string like a list of characters.

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And so in the first loop, the AI will have to value T and so on and so on.

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So that's pretty cool.

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Now what I want to do next is I want to restore or redo this example of the while loop with the if statement,

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also with the for loop.

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So since it will be pretty similar, let me just copy this and now we have to modify it.

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And of course, we have to modify this one.

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I think the rest can be, yeah, can be as it is.

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So what we do is we ride for AI in and now we must make a list basically from one to and so on until

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10.

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And this is, of course, a bit tedious.

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So maybe let me start it.

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And for now, I mean, it's OK as only 10 numbers, so I can show you what happens

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for this one.

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So like this?

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So now we have the same output as before.

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So you see, it works.

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But a trick that I want to show you is, how can you optimize this long list here?

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Because if you would say, I want to do this for the first 1000 numbers, then it would be very tedious

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to write all of these numbers down in a nice way.

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To construct such a list is to range commands.

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So the range command works like this.

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You basically give a starting value and you give an end value and then it takes all the numbers and

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creates a list out of it.

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So if I run this, it gives me almost the correct result.

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It starts with one and ends with nine.

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So this is once again the same problem as we have encountered before.

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We have to take the ending index one number higher.

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So like this, by the way, you could also leave out the first number.

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But then the I would start at zero, which is not what we want.

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So we just tried one 11 for the range arguments.

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So I think that's pretty good.

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So we have now discussed the while loop and we have also discussed the for loop.

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And the only thing that is left that I want to show you is I want to show you how you can like very

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easily easily store these outputs in a list.

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And for this, you just write something like store storage or store list and make it an empty list,

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which would be this one.

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So just to square brackets which indicate that this one is a list which has no entries yet, and then,

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for example, you can just write for I in range of the numbers one, two six and what do you want to

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do is you want to now append the number to the list.

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So you write store list, dot append and then you write here what you want to append.

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And for example, I want to attend the square of these numbers.

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Are on this, and you see, now we have stored these numbers in the store list variable.

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So here you have square numbers one, four, nine, 16 and 25.

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And in the following, we will work further with lists and with loops.

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And I want to show you how you can store this information in files and how you can load the information

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back into your notebook.