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Welcome back, everyone.

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We're now going to switch gears and our discussion of control flow to begin discussing loops.

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We're going to begin with the for loop.

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The term enterable means you can quote unquote iterate over the object.

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So what do we mean by iterate?

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That means that for every item in a sequence, you can perform an action.

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So, for example, remember that a string is a sequence of characters so you can perform an action or

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use every character in a string.

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Or you could iterate over every item in a list that is perform an action for each item in the list or

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use each item in the list.

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And you can even iterate over every key in a dictionary.

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So let's talk about the syntax for for loop.

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This is what the typical syntax for for loop looks like.

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Here I have my interval as a variable.

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It's equal to a list and then I'm performing the for loop.

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Let's break down what's happening here.

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So first, I'm actually assigning an interval object here.

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We can think of sequences as the adorable object here, and we have a list of one two three.

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Besides that variable, then you actually get to choose the name of a temporary variable that is going

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to be the placeholder for each item in that list.

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So it's going to be either the one, the two or three, and you're going to say for each item in that

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list in my interval.

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So note the syntax here you say for your made up variable name in then your object, you perform an

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action.

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This is a very simple action performed here, just printing out the items in the list.

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But that's all we need to do here to see the results.

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One two three.

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Notice how they are on separate lines each one.

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So it's going one at a time through each item in that list.

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Let's check this out in more detail in our code editor.

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OK, so we're going to do is just practice looping through an object so I can create my list here.

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And I'm going to say this list is the let's say, numbers one, two, three, four or five.

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And then how do I iterate through this list, I simply say for.

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Item in my list, Colon.

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And note, when you had colon enter, you're actually going in the patient.

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And so what's going to happen is I'm going to have this block of code execute for every single item

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in that list.

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So I could say go ahead and print out the item and note that this is technically just this little temporary

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variable.

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So if we save this, I should see one print it out.

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Then two, then three, then four and five.

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So we go ahead and run this.

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And there you have it one, two, three, four or five.

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Now what's interesting here is you can call this temporary variable whatever you want.

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So you can call it for jelly in my list.

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Go ahead and print jelly.

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I just want to make it clear that it's totally up to you what you call that variable.

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So if I run this code again, it still works just fine one, two, three, four or five.

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The other thing I want to note here is that you don't necessarily need to use the actual item in the

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list.

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This is just saying for every item in this list, go ahead and do something.

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So if I said for item in my list print.

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Hello.

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Then it's just going to print hello.

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Five times.

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This is just to give you the idea that you don't necessarily need to use each particular item in the

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list.

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Now what would be kind of a good use case for this?

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You could say something like.

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Prince, let's imagine that these were our sales numbers, so we can say for numb in sales just to give

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you an idea of kind of how you would set up a for loop.

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We have some sales here, one through a five four number in sales.

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I can use again if string literal formatting and say sales, for example.

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Sale of and then in curly braces person and um.

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Save that change and then run this, you see example sale one two three four five.

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OK, so that's the very basics of a for loop on a list.

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Again, you just set up the adorable object and then say for whatever temporary variable you want in

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that object, then you execute this block of code.

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It doesn't have to be a one liner here later on.

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This will be a more complicated.

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Now, I should note, this works the same for tuples.

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So if this were actually a tuples, so if I just change the square brackets for a tuple here, that's

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also totally OK.

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This will actually work just the same.

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Now what happens if this is a dictionary?

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So let's kind of set up a dictionary here.

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I'm going to say.

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Employees.

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Is equal to.

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And then let's say our CEO.

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Is Cindy.

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And let's say our CFO.

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Is.

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James.

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OK, then what's going to happen is if you loop through a dictionary, it's going to loop through the

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keys.

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So for key in.

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Employees.

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Let's say print the key.

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Just so we can explore what happens here.

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So we should expect to see CEO and then followed by CFO.

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OK.

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If I actually want to grab the value here, Cindy and James and print that out, I could be a little

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clever and say the following I could say.

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Employees and then grabbed the item at that particular key, so it actually pass and see you back into

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employees as it loops through these keys.

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And then we see Cindy and James.

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And so it would probably be better terminology here would be for position and employees.

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And then let's actually use both of them.

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I can print out using f string literals here.

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I can say.

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The.

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Position, let's make sure we use curly braces.

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The position.

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Is held by and then will actually then look up the employee inside the curly braces employees.

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At that position.

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OK.

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So again, let's break down what's happening here, I have this dictionary and I know when I loop through

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dictionaries, I actually have the keys.

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In this case, the keys in my dictionary employee stands for position so I can say the position it employs

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and then print out this string literal and her position and then look up who is the employee at that

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position.

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Hopefully, it's beginning to kind of change some gears in your mind or get those spinning.

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I can see the CEO's hold by saying the CFO is held by James.

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The last thing I want to point out is there is something called tuple unpacking.

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Remember, I said that it's really common to return back items in the forms of tuples and we can actually

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see a list of tuples as a result often.

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In fact, if you print out employees the items.

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Open close parentheses there and run this, I can see an actual list of tuples.

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Remember this the key value pairs.

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So because this is such a common way of returning back items, a list of tuple pairs.

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There's something called tuple and packing, and I want to show it to you now, just so it's not a complete

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surprise when you see it later.

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So I'm going to make a little artificial list and let's say my list.

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Square brackets.

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And then I'm going to set up some key value pairs.

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So I'm going to say a b.

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Comma.

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And then say, see the.

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So let's actually make one more here, just so it's really clear.

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And let's make this last one.

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One.

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Let's just say one and two.

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So what's happening here?

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I have a list.

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And in this list, there's three tuples.

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So I'm just going to space them out a little bit.

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So you can see clearly what's happening here.

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I have the three tuples, A, B, C D and then one two.

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Now look what happens if I were trying to.

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Iterate through this list for item in my list.

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Prince item, we should expect that to actually print each tuple and there's three pupils.

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And there it is, a b c d one two.

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But what if I actually wanted to get individual elements from those tuples, let's say only wanted a

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C and one and only one of the first items.

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This is where tuple and packing comes to play.

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Instead of writing something like item, I can write a little tuple here and say key or let's say,

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item one and then item two.

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And then I can specify I only want a printout.

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Item one.

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So this is known as tuple unpacking.

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Now, this only works if you know for a fact that in your list, you're getting objects returned back

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as tuple pairs like this.

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And this could extend if you have a third item in the tuple, you could say Item three, etc. But for

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now, we're just going to say I don't want item to.

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Go ahead and print this out, and we would expect to see a sea in one.

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And there it is, a sea and one because I'm saying grab the tuple items, but only print out item one.

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And technically speaking, you don't actually even need these parentheses here.

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So you typically don't see tuple and packing like this where just says four and then tuple item one

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comma tuple item two common to bottom three, etc. in my list.

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Then you can do something here and you can actually then print them out on separate lines so you can

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do whatever you want with these, so I can print out.

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Item one, then print out Item two, so take them over here and just think, what would you expect the

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output of this to be?

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Well, it's going to print out a then B, then C then D than one than to remember because it's going

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through each of these tuples.

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One at a time.

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Let's actually see the results here.

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And there it is, it's a then B, then C, then the then one and two, because remember, it's still

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going one two at a time.

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It's just up to you.

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Which items are printing out in which order?

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OK, so that's the very basics.

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A for loop.

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Main thing to understand is, do you have the four key word?

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Then you choose some temporary variable name in and then often we'll be dealing with this.

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But you can do this for many different types of objects and then you execute a block of code each time.

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And as you mentioned, technically, this block of code does not need to be related to the items in

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the list.

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I can still say something like prints.

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Hello.

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And this would still work, it just prints Halo three times, so I see.

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Hello, hello.

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Hello.

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OK.

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And that's it for four loops coming up next, we're going to talk about while loops.