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Let's talk about conditional logic, an important concept all over programming.

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What do I mean by conditional logic?

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We've learned about booleans, right?

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We have true and we have false.

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And some of you might be wondering why they're so useful.

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And when it comes to conditional logic, booleans are really, really important.

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For example, let's say we create a variable is called.

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And you know what, we're going to create a car that automatically detects if you can start the engine,

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maybe if you're not old enough, the engine won't start and it won't let you drive so that they make

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sure that this car is super safe and only people that are perhaps over 18 can drive it.

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So how can we code something like that?

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Let's assume Tesla has a new feature like the.

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Well, we'll have something like is old and we'll set this to.

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True, right?

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Maybe we have something else, maybe it checks the license to make sure that we have a license so we

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can say is license.

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And then we can set it to true.

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Now, this could change.

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True and false, depending on the user and the driver, but when I talk about conditionals, this is

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what I mean in Python, we can use the if key word to say if some condition exists.

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And this is just me writing it, it doesn't exist.

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So you can see that I get a read and underline with invalid syntax.

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But here we want to say a condition that evaluates to true or false.

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In our case, we can say, hey, if this is old, which what does it evaluate too well evaluates to

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true.

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If that's true, then let's say print.

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You are old enough to drive.

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Now, there's a few new things here.

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One, I've added a semicolon or a colon.

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And then you'll see here that the indentation is different.

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As a matter of fact, when I press enter.

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After the Callon, you see that it automatically gives me a space, this tells the Python interpreter,

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I'm going to do an if statement, a conditional operation, and if this happens to be true, run everything

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that's inside of here that has this indentation.

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And if I do something without the indentation, let's say print.

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This to the Python interpreter is like a completely new line.

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It is not part of this F block and if you're using the ripple you see over here, I get a little minus

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sign, fight, click this.

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You see how it hides.

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Well, what it does is it's saying, hey, this is a code block over here, it's an entire thing in

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itself, but anything outside that is not indented well doesn't belong to it.

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So to a Python interpreter, it's going to say, I have this line and then I have this line.

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Let me show you what I mean if I run this program.

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I get you are old enough to drive and then I also get check, check.

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But what if I say is old is now false?

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What do you think will happen?

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If I run this.

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Our Python interpreter is going to say, hey, set variable is old to false, hey, that is licensed

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equals to true and then it's going to go to line three.

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No, nothing there.

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I'm going to keep going like for hey, if is old.

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Is this true.

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No.

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If all this false and the interpreter is going to say, OK, I'm only supposed to run this piece of

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code if this is true because this is now false, I'm just going to completely ignore what's underneath

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here and just go to the next line that has, well, no indentation.

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So it's going to print, check, check.

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And this is the power of conditionals.

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We're able to essentially skip lines.

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The interpreter doesn't even care what's in here because I just told my program to skip from line four

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to line six.

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How cool is that?

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So we learned that there is this if keyword, but there's also another thing we can use called else,

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and you'll notice here that I did and added to the indentation.

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And else, as the name suggests, simply says.

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Hey, if this something is true, then do this otherwise also else do this and again, you see that

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I've added the indentation.

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So try to guess what's about to happen in this program if I click run.

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I get check, check because it's saying, hey, is old, is that true?

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No, it's not true.

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OK, I'm going to completely ignore that the interpreter sees else.

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OK, well, this wasn't true.

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So I'm going to run whenever this evaluates to false, I'm going to always run, print, check, check.

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What if I change is old to now equal to true?

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What will happen next?

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Well.

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I get you are old enough to drive.

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Else only runs if the if block of code evaluates to false.

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Very, very cool.

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All right, let me ask you another question, what if I did print here?

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And let's change this to you are not of age.

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If I run this.

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Is that what you expected?

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Well, I hope by now you agree that this is the expected behavior because is old is true.

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I'm going to print this and then Python interpreter is going to say, well, this was true.

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So I'm going to completely ignore the else block and then just go to the next line.

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What's on line eight?

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Nothing.

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So I'm going to go to line nine and I'm going to print.

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OK, ok.

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OK.

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As you can see, we're now controlling the flow of our programs where instead of going from one to nine,

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just line by line, we're now saying a line for do some sort of check.

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And based on that, skip a few lines.

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Very, very cool.

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All right, there's one other thing I want to show you, and it's the L if.

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And I know this kind of looks weird, you would think that it will be else if but no, no, no.

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It's if.

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And what do you think this does?

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Well, you use it in combination with if you say if something.

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If otherwise, else, if another condition, so let's say, is licensed.

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Then do another condition, so let's say print, you can drive now.

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So let's go through this again.

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I'm going to say, is this person old enough if that person is old enough and this evaluates to true,

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well, then I want you to.

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Run this otherwise.

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I want you to run this condition, hey, is this true?

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No, if it's not true, then jump to else.

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So what will happen here if I click run?

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We get true for the first conditional block right over here, so automatically Python interpreter is

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going to say, well, we just got through here, so I'm going to ignore this and ignore this and then

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print, OK?

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OK.

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But let's say that is old is now false.

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What will happen next if I click run?

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This is false, so Python interpreter is going to say, nope, not going to care about this block and

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I'm going to go, hey else if I condition Hey, is this person licensed?

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Yep, they are.

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So I'm going to print.

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You can drive now and ignore or else.

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So it works like this.

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What if both of these were false?

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Well, as you can imagine, the Python interpreter is going to ignore it's going to run this say no,

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this is false.

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This no, this is false.

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And then finally, it's going to run this.

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You see that else is a catch.

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All that is, if none of these conditions are true, then we're just going to run this.

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So it's a back up in a sense.

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Hey, if all things fail, then just do this.

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Very, very cool.

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Now, if you look at this program, you're thinking this program doesn't really work that well, does

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it?

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I mean, we're checking if the person is old and if a person is licensed.

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But shouldn't we check both?

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We want somebody who has a license and who's old enough to dry.

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Hmm.

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This is this is a buggy program.

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If we implement this in a Tesla, well, we're going to get a lot of lawsuits, right.

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Because we can get somebody who's maybe licensed but isn't old enough, which I guess doesn't make sense.

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But we can get somebody who is old enough but never got their driver's license.

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And somehow we get access to the car and they can start the engine and drive in.

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Oh, that's a that's a lawsuit waiting to happen.

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So how can we fix this?

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You know what the power is that this is an expression, right?

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An expression, if you remember, is something that produces a value.

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And that means that this doesn't have to, you know, just have true here, it could be an expression.

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So I could say if is.

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Old.

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And is licensed.

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Then I can do that, and this is something new that we haven't seen before the end, this is another

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key word in Python.

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And in an upcoming video, we're going to talk about more of these keywords.

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But this should be like English, right?

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If is old and is licensed, then do this so we can now remove the L.F..

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And then here.

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Both expressions need to evaluate to true, that is whatever happens here, this has to evaluate to

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true and this has to evaluate to true and only when both are true again as and states, then you're

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old enough to drive and you have a license.

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So that if I run this.

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Well, I get an error rate because or not an error, but it goes into the else block because both of

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these are false.

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If only one of them is true and I click run.

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You are not of age because both of these have to be true.

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If I click, run.

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Hey, all right, the car is starting, you can drive away with your Tesla.

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OK, before I finish this video, because this is a lot, I want to just note one thing that is the

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L if statement.

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The live statement is really, really useful because when you have a code like this where you have an

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IF statement and an El statement.

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Usually you only see one of each.

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I mean, sure, in another part of the program, I could have another if statement and an if statement

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with another false statement inside of you.

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But usually when you have this grouping together, you only see one F and one else, but you can have

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multiple LFS.

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So I can have L.F. another condition here and then I can have another L.F., another condition here

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and you can have as many as you want.

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Eventually the is going to either evaluate one of these conditions to true or it's going to go into

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the else block.

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But usually you follow this order.

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All right, that was a lot.

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Let's take a break and explore this topic a little bit more.

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I'll see in the next one, Pabai.