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Hello.

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Welcome to another lecture of our python course.

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And my name is Stephan.

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In this lecture you will learn about conditions, but you will also learn if Elif and else chain.

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So often you will need to test more than just two possible situations.

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And to evaluate these you can use python's if Elif else syntax.

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So Python executes only one block in an if Elif else chain, so it runs each conditional test in order

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until one passes.

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So when a test passes, the code following that test is executed and Python skips the rest of the tests.

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So many real world situations involve more than two possible conditions.

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For example, consider a bus ticket, a mechanism bus ticket technology that charges different rates

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for different age groups.

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For example, bus tickets for anyone under age eight is free bus ticket for anyone between the ages

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of eight and 18 is $50.

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Bus ticket from anyone age 18 or older is $90.

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So how can we use an If statement to determine a person's bus ticket rate?

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So this code we will write here.

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For example, let's make the my age here, for example.

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My age is 25 for and we will change this age to test different conditions.

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If our age is here, let's actually let's actually write the first statement here.

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So if a ticket for anyone, a bus ticket for anyone under age is free.

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And so if age is less than eight, then we will print.

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Your.

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You need to pay.

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$0.

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Or.

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Yeah, let's actually, instead of writing that your ticket is free here.

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And.

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Here of my age.

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And after that we will add else if I will explain all of this here else if Elif here, Elif my age and

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here, let's let's actually take this.

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Here.

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So we did this.

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Now.

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Now we are.

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We need to do the second here.

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So bus ticket for anyone between the ages of eight and 18 is $50.

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Now we will write that.

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So if my age is less than.

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Here.

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Anyone between the ages of four and 18 is $50.

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And here we will write 18.

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My age.

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18.

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So you will explain here.

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You might be wondering why we didn't included eight here, which I will explain now after writing this

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code and you will understand because here print we will use your ticket.

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Ticket is.

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Bicycle, $50, $50.

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And after that, we will also add clouds here and here.

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Print.

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So your ticket is $100.

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So also we did this section.

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Mark This one.

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That's it.

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So firstly, the if test checks whether a person is under eight years old.

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So when test passes, an appropriate message is printed and Python skips the rest of the tests.

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And here, let's try this for example, if my age was five.

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And here, as you can see, your ticket is free and the life line is really another if test so which

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runs only if this previous test fails.

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So in this case it didn't fail here and this code didn't run.

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So at this point in the chain, we know that the person is at least eight years old because the first

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test.

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Uh, is let's actually, uh, make here.

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Now, in this case, we know the person is at least eight years old because the first test didn't run

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right.

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So if the person is under 18, an appropriate message is printed and Python will not execute the else

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block.

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Now, Python will now execute because our Elif here, our Elif is executed, but also our if didn't

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execute because it didn't meet meet the conditions here because my age was ten.

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And.

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Here if my age under eight, then it didn't print because my age is not under eight.

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You learned that in expressions previous lectures, and here we have Elif, which is my age, is under

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18 and here we have ten here.

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So in this example here, the if test, let's actually yes, here in this example, the if test evaluates

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false so it's code block is not executed.

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However, the Elif test evaluates true which is the ten is less than 18.

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Right.

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So its code is executed.

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So the output is one sentence here informing the user that admission cost is $50.

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So your ticket is $50.

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Any age greater than 17 would cause the first the if and Elif tests to fail in this situations here,

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let's actually make it 20 In this situations the else block will be executed here and as you can see

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here else block is executed.

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This block is in the if and Elif didn't execute because they didn't meet the condition here and here

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we have the else block executed here.

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And we printed this message here.

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So rather than the printing the ticket price with the if else block, it would be more concise to just

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set the price inside the if else chain.

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And then we have a single print call that runs after the chain has been evaluated.

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So now we will let's delete this and we will do another example with that.

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So here, if my age is 20, remember that the.

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For under a under age of eight, it will be free for bus ticket.

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So my age will be or and we will also add price here.

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Price is going to.

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Zero and my age eight while my age is other than 18.

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Then the price is going to be price.

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Price is going to be 25, the 50 and else if our age is greater than 18, we will praise we will use

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the price 19 here.

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And after that we will print here we will use format.

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Your bus ticket cost is here and we will use this price.

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That's it.

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So here, let's run this.

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And here we are.

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Our age is 20 and our else block is executed here.

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So the indented lines here you see here, these are the indented lines set the value of price according

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to the person's age, as in the previous example.

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So after the price is set by the if here, if Elif and else conditions as separate on indented print

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call uses this value the price value.

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Um, two.

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So price value.

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To display this message, right?

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And so this here, this code produces the same output as the previous example.

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But the purpose of the if Elif else chain is narrower.

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So instead of determining a price and displaying a message, it simply determines the ticket price.

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And in addition to being more efficient, the reveals this code here is easier to modify than the original

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approach that we did in earlier in this lecture.

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So to change the text of the ultimate message, you will need to change only this print call rather

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than three separate print calls that was here before.