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If by now you've been following through the last few videos

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of basically learning about comparison operators and multiple

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comparison operators together, you might have already run

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into a particular issue where you could say, 'name = "Kalob"',

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and then what do you do if you're looking for a specific

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'name', or what do you do if you're looking for a specific

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'name', and nothing else matches?

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So right now, we could do 'if name == "Kalob": print(

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"Name is Kalob")'

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But what if the 'name' is not "Kalob"?

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Then we would say, 'if name == "Henry": print("Name is Henry")'.

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But what if 'name' is not "Kalob" or "Henry"?

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Then we could say, "if name == "Zephyr": print("Name is Zephyr")'.

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And let's run that. It says, "Name is Kalob".

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And if it is "Zephyr", then cool,

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it's going to show up as "Name is Zephyr".

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But what if it's none of those names?

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What if the name is "Ezra"?

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Nothing happens.

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What if we wanted to catch that,

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or what if we want our program to not have to evaluate every

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single one of these lines?

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We just want it to match one.

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So if the 'name = "Henry"', well, it should only match this one,

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but still it's going to try to match this one,

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it's going to try to match this one,

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and even if it does find a match, it's going to find

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this ones. We've actually run into two problems here, where it's

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going to continue to execute these 'if' statements, even though

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they are sort of related, and we don't want them to be.

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And if it does not match "Kalob", "Henry", or "Zephyr", what do we do?

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So, I'll just rerun those, and we'll say the 'name = "Henry"'.

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Now, when we get two chaining operators together, we have

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these things called 'if-else' statements, or 'else-if' statements.

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So we can say 'if name == "Kalob": print("Kalob")'.

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We can also say 'elif name == "Henry": print("Meow")',

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because that's one of my cats.

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'elif name == "Zephyr": print("Little meow")', because

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he has a tiny little meow.

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He's got a tiny voice. And we're going to see that it just says "Meow".

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Now, the nice thing about this is Python is going to try

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to evaluate this and says, "You know what,

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the name was not Kalob,

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the name is Henry", as we can see here.

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Okay, so it's going to execute that one, and then it gets to the 'elif',

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and it says, by the way, 'elif' is short for 'else-if' in Python.

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So the 'elif' is saying, "If the name is then equal to "Henry",

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print me out". Now, this turned out to be True.

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The name was "Henry".

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And so Python said, "Oh, okay, the name was Henry.

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I do not need to execute this.

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I don't need to check it".

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Now, Python is very fast when it comes to checking 'if' statements.

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So like, you're not going to get massive performance boosts,

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but when you are writing code that is connected, this is

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a lot cleaner, because now if I wrote this and another Dev

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came in and said, "Oh, what is this looking for?"

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They could say it's looking for "Kalob", or it's looking for

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"Henry", or it's looking for "Zephyr".

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We're up here.

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It's looking for 'name' is "Kalob",

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'name' could also be "Henry",

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'name' could also be "Zephyr".

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There is a little bit of a syntactical difference there,

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but it is also important just for reading the code.

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Now, what happens if the name was not "Kalob", "Henry", or "Zephyr"?

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What if it was any other name?

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What we could add in here, an 'else' statement, and an 'else'

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statement does not take a comparison operator.

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It just says if it is something cool, if it's not, if it

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is literally anything else, execute this code. It will say,

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print in here with an 'f""' statement.

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'print(f" The name is ")'.

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Now this still result in "Meow", because I have to go and change that

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'name', and I'm not going to change it up here because I

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like this example, but I am going to overwrite it right here.

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'name = "Ted"'.

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And let's go ahead and run this.

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It says, "The name is Ted".

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[no audio]

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"Kalob". Yep, shows up as, "Kalob". "Zephyr", it's "Little meow" because he's got

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a little meow or 'name' is "Literally anything else in the entire

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world". That does not match "Kalob", "Henry", or "Zephyr".

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Just go ahead and run this.

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And it says, "The name is Literally anything else in the entire world".

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Now, you don't actually need these 'elif' statements either.

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You could say 'name =', let's not do 'name',

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let's do 'age = 25',

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and you could say, 'if age < 21':

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print("Nope, not allowed to have alcohols")'.

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Otherwise, if you are older than 21, 'print("Welcome to the bar,

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what are you drinking tonight?")'

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[no audio]

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And just like that, Python is going to say, "Okay, the age is 25.

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if age", which looks like this, "if 25 < 21",

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Nope, it is not.

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So it's not going to execute this.

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It just says, "I'm going to get here.

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Nope. That's False.

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If False, no". Comparison operator is always looking for True.

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So it skips over this and then goes straight to the 'else' statement,

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and the 'else' statement says, if it is literally any other answer,

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doesn't matter what the answer is, it is the opposite of

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this. And so to catch any sort of special cases, we use an

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'elif' statement.

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But if you're just looking for something simple, like if

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you're allowed to drink alcohol or if you're allowed to vote,

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all you need is an 'if-else' statement in here.

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Now you're going to be writing a lot of these

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in, well every programming language. Python is no different in that

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case, just because this is how you tell a program what to do.

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If something is something, do something, if it is not

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do something else.

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And programs are made up of hundreds, thousands, millions,

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maybe even billions of 'if' statements, depending how big the

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program is.

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Google probably has a good example of billions of 'if' statements

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in all of their source code.

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But what I'd like you to do as quick little hands on example,

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is I want you to set a number, check if that number is a certain

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number. So I'm going to let you write your own 'if' statement

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here, and also write an 'else' statement,

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and then I want you to change your variable number so that

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the first statement is triggered, and then the second statement

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is triggered, but not at the same time.

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So one should run, and then you change your variable, and

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the other one should then run.

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Go ahead and give that a shot,

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and when you're done let's head on over to that next lesson.