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Booleans
7:51Let's take a look at boolean literals True and False and how to use logic
A boolean data type only has two
valid values, true and false.
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These values are gonna be use heavily in
the code that we create from here on out.
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There are many times where
we'll wanna ask a yes or
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no question and then run different code
based on how the question's answered.
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Booleans are named after their creator,
a mathematician named George Boole.
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In George's algebra, he used ones
to represent the value true and
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zeros to represent false.
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And this is the reason you see actors
playing hackers in movies dealing with
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ones and zeros.
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There's a popular saying in this world
that says, it's all ones and zeros.
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And that's because it is.
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Electrical circuits used in
the computer you're using right now,
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are using boolean values, on or
off, true or false, one or zero.
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So, they seem pretty important
to get a handle on, right?
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We should explore these, true or false?
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The answer is true.
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There are only two boolean literals,
true and false.
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A variable can refer to the boolean result
in an expression like our in keyword.
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For instance,
has_taco = is taco in catacombs.
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You'll see that that was stored.
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Has_taco, is stored true in there.
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And just like our other data types,
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you can actually coerce
values to be true or false.
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It's called bool and
as you probably guessed,
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bool(1) is true and
of course bool(0) is false.
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Now here's something
that might surprise you.
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In addition to being the answer to
the meaning of life, 42 is also true.
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In fact, any non-zero number is true,
and zero is false.
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So, what happens with the string?
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So if I say,
what's the boolean of burrito.
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Now I guess speaking personally in
this statement, I want a burrito,
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is always gonna return true, but
that's not why this is true.
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What's happening here is any
object that isn't empty is true.
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Now, empty is an interesting concept
that we haven't talked about just yet.
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So, a string literal is a pair of
quotes surrounding a character, right?
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But what if there aren't
any characters in there.
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Now this is known as an empty string,
and as you can see, it's false.
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This emptiness is false,
tends to be a common confusion point for
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developers, so
I want to introduce you to another term.
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The way in which a value coerces
to a boolean also has a name,
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it's truthy or falsey.
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So, for instance,
I can say that empty string is falsey, and
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the number seven is truthy.
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I know it sounds like I made that
word up but I assure you it's real,
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and you'll see it and hear it used.
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I guess it's slightly better than
saying it's true-ish or false-ish.
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So all that to say, emptiness is falsey.
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[LAUGH] Sounds like
the name of an emo band.
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I'd like to introduce you to a couple
of keywords that you already know and
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use in real life.
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You are about to see some of
the beauty of Python's readable syntax.
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So, if I wanted to negate a boolean value,
you know,
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get the opposite of the value,
I can use the not keyword.
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So I can say not True, and it says False.
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Neat, right?
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And if I say not False,
we'll see that that's actually True.
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So next up, you can actually chain
together booleans using the keyword and.
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So if we say, True and True,
we see that that's True.
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The way that and works is that both
booleans on both sides of the and
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must be true.
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So, you can keep chaining them together,
too.
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And it works just like order of
operations on our math examples,
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it goes from left to right.
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So if I say True and True and
True, we get back True.
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But what happened was it checked this
True and True, and that returned True.
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So that True, the result of this was
checked against this, True and True and
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both sides were true so
therefore it's true.
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But, if we come and we slap a false
at the very end, and False.
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We'll see that it's false because all of
this became true, and then we had true and
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false, and both sides must be true
in order for and to return true.
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And it wasn't, so it returned false.
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So ors work a little bit different.
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If either value on either side of
the keyword or is true, it's true then.
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Ands work with both and
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ors work with either.
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So if it's False or True, we're gonna end
up with True, because there's one true.
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But if we have False or False,
it's gonna be False cuz nothing's true.
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You can chain ors together too and you can
also use parens just like we did with our
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math to help it be more specific
about the order of what's happening.
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So let's just go ahead let's
build something random.
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We'll say (False or False or
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True) and (True and False).
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Okay, so let's walk through it
before we press Enter here.
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So, two falses or'd together that's a false.
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So we have a False or True.
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One of those is true, so we have a true.
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So True and, and (True and
False), so this is a false.
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So we have True here and
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we have False over here because
not both of these are true.
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So we have a False and
a True, that should be False.
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Because both sides need to be true.
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And remember, we can always negate.
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We come in here, we can say, and not.
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Now you'll see that it looks
like I typed over the front.
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This is a bug that sometimes
happens in the REPL.
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So I'm gonna press Spacebar.
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Even though that looks wrong, watch.
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Press Enter, it came true.
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If we look at it, there it is.
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So we have false, or
false, or true and not.
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And so that negated this last one here,
so this not true or false, true and
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false was false.
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Not false is true.
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I know that this is all
a little bit abstract.
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So, let's try to make this
a little more concrete.
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Let's think about a dating app.
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And let's try to imagine some
code that might exist there.
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So, Heidi has some kids.
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And she'd like to find
someone who has kids too.
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But she can't stand smoking, she abhors it.
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So, let's fill out a profile for
a parent on the site who's also a smoker.
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So, is_smoker = True, and
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their parents, so has_kids = True.
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So Heidi's requirements look like this.
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She says I want somebody who's a parent.
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So he has_kids and is not a smoker.
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So, we have in this particular situation,
for her requirements, this profile here,
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we have has_kids, that's true and
not is_smoker, so that's false.
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So we have true and false,
that's a false, that didn't work out,
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Heidi is gonna swipe left.
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That's just isn't the one for here I
guess, here's hoping that she finds her.
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Do you see the power of booleans?
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They can help you to find true love.
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Now, to really fall for booleans, I'd like
to show off the ability to run different
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blocks of code based on their value.
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This is called conditional branching.
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Let's branch off to that topic,
right after this quick break.
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