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Instructor: Welcome back.

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In this video, I wanna talk

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about the idea of truthy and falsy.

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What do they mean?

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And you'll hear this a lot in Python programming.

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You see, up until now, you've used booleans here as values.

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So it was really easy.

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If true and true, then run this code.

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But Python can do other things as well.

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For example, if this was five and this was, let's say hello,

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what do you think will happen here in our program?

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Well, if I click run,

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you are old enough to drive

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and you have a license, is that what you expected?

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And this is because what Python does

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underneath the hood is actually convert these

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to booleans for you.

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So it's almost as if

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it is doing this, remember type conversion.

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We're converting the type

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to boolean

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as soon as we get to this if statement

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because Python is saying, Hey

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I want true or false, I don't care

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what is old is

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I don't care what is licensed is just gimme true or false.

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So I know whether to do this or to go to the else block.

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Now, if I was to just print,

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let's do this here.

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Let's do print

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boolean

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hello.

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And then finally print boolean

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five.

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Let's see what we get.

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We get true, true.

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And this is what we call a truthy value in Python.

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That is, it's a truthy value because if we run the boolean

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type conversion on it, it evaluates into true.

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What's a falsy value?

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Well, if I do zero, and if I do, let's say an empty string

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and I click run,

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those are falsy.

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That is, it's not actually false, but it is falsy because

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if we run boolean on it to Python, it's going to say, Oh

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this is false and zero.

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That's false.

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And that kind of makes sense, right?

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And if you actually go to Stack Overflow, if you've never

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seen Stack Overflow before, if you ever have programming

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questions and you're Googling them, usually the top five

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answers we'll contain either one or two

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Stack Overflow answers.

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And basically what happens is people ask questions like,

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What is truthy and falsy and Python?

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And you get answers.

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So you can see over here that it has four answers

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and you usually look for the check mark, which means

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that this is a verified answer.

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It means that, hey, this question owner has accepted it

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as the best answer.

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So the person who asked this question just said, Yep

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this is the right answer.

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This is the best one.

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But you also have other people voting.

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So you can see that this answer received 46 marks.

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And although it was marked

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as the correct answer by the user, maybe somebody else came

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along later on and gave an even better answer.

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So now we have 123 up votes.

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And you see that this answer is a lot better.

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All values are considered truthy except for the following.

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So you can actually see here that in Python

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these values are considered falsy.

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You can see zero here, you can see an empty string here

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and then there's a few other ones.

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Empty set.

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You have a empty dictionary, empty list, empty tuple.

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You have decimals, you have things like fractions.

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You have 0.0.

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False is that.

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And also none is falsy.

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So that if I type in none here,

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that's false too.

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Now, you don't need to memorize these

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because most of the time it, it makes sense, right?

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But it helps us do conditional logic very nicely.

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For example, let's remove this.

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And let's say that we have a user

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and this user has to have a password and a username.

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If let's say the username is

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Johnny

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and the password is 1, 2, 3.

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Well, instead of me saying,

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Hey, if this user has password and username

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and we're not checking if the username exists

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or password exists, we just wanna make sure,

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hey did this person fill out the form

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and did they try to submit a username and password?

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I can just simply say password and username

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and I don't have to worry

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about converting this to a boolean or anything like that.

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Because if password and username exists

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then try to log them in.

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And you see that it reads a lot nicer

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because each one of these get evaluated

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into a truthy and falsy value.

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It's a nice little feature to keep Python,

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well, nice and simple, and reading like English.

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I'll see you in the next video.

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Bye bye.