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Now that we are happy with the way the code looks, we're ready to add more features to the program.
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One thing that I need is very important, and that the program is lacking is checking if the user is
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actually inputting all the required arguments.
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So we know that the program will not work if the user does not input an interface or a new Mac.
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But if someone goes to the terminal and for example, runs the program by saying mac changer, I had
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zero and not give a mac, you'll see that python will just throw an error.
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Now to us, this is useful as a programmer, but to the user this is not nice at all.
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We want to display a meaningful error to the user telling them that you forgot to give us a mac address.
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Please make sure you input a mac address.
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Now, in order to do this, we need to implement some decision making in our program.
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We need a way to check and make sure that the user entered a value for the interface and also entered
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a value for the Mac.
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To do this, we'll need to use an if statement.
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So in this lecture we're going to have an introduction on what if statements is what decision making
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is, and in the next lecture will implement it in our program.
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Now when we talk about decision making or if statements, we're talking about executing code only if
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a condition is true.
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So we're going to first check if the user entered a value for a mac address and only print an error
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message if the user did not enter a mac address.
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So we're only executing code based on a condition.
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Now there are lots of ways to come up with conditions.
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You can check if a variable is equal to something.
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You can check if something is greater smaller.
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You can check if a variable exists in the list.
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You can check if something is true or false, and so on.
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As we go through the course, we're going to be using a lot of conditional statements, and all of this
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is going to become very clear to you right now.
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I just want to give you a general idea of what decision making is and some basic examples of if statements.
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And as we go through the course, we're actually going to be using all of these statements, we're going
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to be using lots of these conditions.
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And everything is going to become clear to you by the end of the course.
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Right now.
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I just wanted to have a quick comparison between three common ways of writing an F statement.
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So here on the left, we have the most basic example of an F statement.
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So we do if condition.
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And like I said, a condition can be a lot of different things and we'll have a look on them later on.
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So let's just think of a condition as is.
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So we're doing F condition and then we have a block of code here.
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And this block of code will only be executed if this condition is true.
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Else we have another block of code and this block of code will only be executed if the above condition
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is false.
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So when you run a Python program in this example, it will check for the condition.
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If it's true, it will execute the code here.
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If it's false, it will execute the code in the false block.
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Then, once it's done with this, whether it did the code in the F block or in the else block, it will
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continue with the rest of the code executing it line by line.
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Another example is where we have multiple conditions.
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So in this example we only had one condition we had if condition otherwise do this.
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In this example we can do if condition one, we execute the code in condition one or if condition one
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is false, then we're going to check is condition two is true.
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If it is, then execute the code here and you can keep doing this on and on and on and on.
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Finally, you can use an LS statement to execute code if all of the above conditions are false.
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So let's go over this one more time.
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In the statement, we have multiple conditions.
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It will first check the first condition.
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If it's true, it will execute the code in the first condition block and it will exit everything else.
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It won't check any of this, and it will go directly to the rest of the code.
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If condition one is false, it will check its condition two true.
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If it is, it will execute the code here and exit.
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Go to the rest of the code.
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If all of the conditions are false, it will execute the code in the statement and then go to the rest
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of the code.
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So this is an example of using multiple conditions in one single if statement.
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This example brings me to the third example, which a lot of people get these two mixed up, and that's
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why I wanted to have them side by side.
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I usually like to teach you programming as a program, but I wanted to have these examples here because
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a lot of people get confused with this, and I want to make sure that you understand the difference
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in this example.
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And here we have multiple conditions as well.
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But notice we have two separate if statements.
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This is different than what we have here.
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We have an if, we have an LF and we have an LS.
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So all of this is one if statement in here.
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This is two separate if statements.
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So what happens is python checks for condition one.
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If it's true, it executes the code here.
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Even if it's true and it executes the code here, it will check condition two and if it's true, it
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will execute the code and condition two as well.
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So unlike this example, if condition one is true, Python will go to the rest of the code directly
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and want check for the rest of the conditions.
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Whereas in here these are two separate if statements.
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So if condition one is true, the code here will be executed.
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If condition two is true, the code here will be executed as well.
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You can also use ls ifs in here.
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You can use ls with them.
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The reason behind this is these are two separate if statements.
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Now.
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That's it for now.
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I don't want to make this too long.
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I just wanted to have these three examples of if statements in here so that you understand the difference
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between them.
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And in the next lecture, we're actually going to be implementing only one example because it makes
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sense in our case and we'll see why.
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