Heads up! To view this whole video, sign in with your Courses account or enroll in your free 7-day trial. Sign In Enroll
Well done!
You have completed Python Basics!
You have completed Python Basics!
Preview
Let's take a look at boolean literals True and False and how to use logic
Related Discussions
Have questions about this video? Start a discussion with the community and Treehouse staff.
Sign upRelated Discussions
Have questions about this video? Start a discussion with the community and Treehouse staff.
Sign up
A boolean data type only has two
valid values, true and false.
0:00
These values are gonna be use heavily in
the code that we create from here on out.
0:05
There are many times where
we'll wanna ask a yes or
0:09
no question and then run different code
based on how the question's answered.
0:11
Booleans are named after their creator,
a mathematician named George Boole.
0:16
In George's algebra, he used ones
to represent the value true and
0:20
zeros to represent false.
0:25
And this is the reason you see actors
playing hackers in movies dealing with
0:27
ones and zeros.
0:31
There's a popular saying in this world
that says, it's all ones and zeros.
0:32
And that's because it is.
0:36
Electrical circuits used in
the computer you're using right now,
0:37
are using boolean values, on or
off, true or false, one or zero.
0:41
So, they seem pretty important
to get a handle on, right?
0:44
We should explore these, true or false?
0:48
The answer is true.
0:51
There are only two boolean literals,
true and false.
0:52
A variable can refer to the boolean result
in an expression like our in keyword.
0:58
For instance,
has_taco = is taco in catacombs.
1:03
You'll see that that was stored.
1:10
Has_taco, is stored true in there.
1:13
And just like our other data types,
1:16
you can actually coerce
values to be true or false.
1:18
It's called bool and
as you probably guessed,
1:22
bool(1) is true and
of course bool(0) is false.
1:27
Now here's something
that might surprise you.
1:34
In addition to being the answer to
the meaning of life, 42 is also true.
1:36
In fact, any non-zero number is true,
and zero is false.
1:42
So, what happens with the string?
1:47
So if I say,
what's the boolean of burrito.
1:50
Now I guess speaking personally in
this statement, I want a burrito,
1:58
is always gonna return true, but
that's not why this is true.
2:01
What's happening here is any
object that isn't empty is true.
2:04
Now, empty is an interesting concept
that we haven't talked about just yet.
2:09
So, a string literal is a pair of
quotes surrounding a character, right?
2:13
But what if there aren't
any characters in there.
2:18
Now this is known as an empty string,
and as you can see, it's false.
2:23
This emptiness is false,
tends to be a common confusion point for
2:28
developers, so
I want to introduce you to another term.
2:32
The way in which a value coerces
to a boolean also has a name,
2:36
it's truthy or falsey.
2:41
So, for instance,
I can say that empty string is falsey, and
2:44
the number seven is truthy.
2:48
I know it sounds like I made that
word up but I assure you it's real,
2:50
and you'll see it and hear it used.
2:54
I guess it's slightly better than
saying it's true-ish or false-ish.
2:56
So all that to say, emptiness is falsey.
3:01
[LAUGH] Sounds like
the name of an emo band.
3:04
I'd like to introduce you to a couple
of keywords that you already know and
3:09
use in real life.
3:12
You are about to see some of
the beauty of Python's readable syntax.
3:14
So, if I wanted to negate a boolean value,
you know,
3:19
get the opposite of the value,
I can use the not keyword.
3:22
So I can say not True, and it says False.
3:26
Neat, right?
3:31
And if I say not False,
we'll see that that's actually True.
3:31
So next up, you can actually chain
together booleans using the keyword and.
3:36
So if we say, True and True,
we see that that's True.
3:44
The way that and works is that both
booleans on both sides of the and
3:49
must be true.
3:54
So, you can keep chaining them together,
too.
3:55
And it works just like order of
operations on our math examples,
3:57
it goes from left to right.
4:01
So if I say True and True and
True, we get back True.
4:03
But what happened was it checked this
True and True, and that returned True.
4:10
So that True, the result of this was
checked against this, True and True and
4:15
both sides were true so
therefore it's true.
4:19
But, if we come and we slap a false
at the very end, and False.
4:21
We'll see that it's false because all of
this became true, and then we had true and
4:26
false, and both sides must be true
in order for and to return true.
4:31
And it wasn't, so it returned false.
4:36
So ors work a little bit different.
4:38
If either value on either side of
the keyword or is true, it's true then.
4:41
Ands work with both and
4:48
ors work with either.
4:50
So if it's False or True, we're gonna end
up with True, because there's one true.
4:52
But if we have False or False,
it's gonna be False cuz nothing's true.
4:57
You can chain ors together too and you can
also use parens just like we did with our
5:04
math to help it be more specific
about the order of what's happening.
5:08
So let's just go ahead let's
build something random.
5:12
We'll say (False or False or
5:15
True) and (True and False).
5:21
Okay, so let's walk through it
before we press Enter here.
5:28
So, two falses or'd together that's a false.
5:30
So we have a False or True.
5:34
One of those is true, so we have a true.
5:36
So True and, and (True and
False), so this is a false.
5:38
So we have True here and
5:42
we have False over here because
not both of these are true.
5:43
So we have a False and
a True, that should be False.
5:47
Because both sides need to be true.
5:53
And remember, we can always negate.
5:55
We come in here, we can say, and not.
5:59
Now you'll see that it looks
like I typed over the front.
6:03
This is a bug that sometimes
happens in the REPL.
6:05
So I'm gonna press Spacebar.
6:08
Even though that looks wrong, watch.
6:10
Press Enter, it came true.
6:12
If we look at it, there it is.
6:14
So we have false, or
false, or true and not.
6:15
And so that negated this last one here,
so this not true or false, true and
6:18
false was false.
6:22
Not false is true.
6:23
I know that this is all
a little bit abstract.
6:25
So, let's try to make this
a little more concrete.
6:29
Let's think about a dating app.
6:32
And let's try to imagine some
code that might exist there.
6:35
So, Heidi has some kids.
6:39
And she'd like to find
someone who has kids too.
6:41
But she can't stand smoking, she abhors it.
6:44
So, let's fill out a profile for
a parent on the site who's also a smoker.
6:47
So, is_smoker = True, and
6:52
their parents, so has_kids = True.
6:56
So Heidi's requirements look like this.
7:01
She says I want somebody who's a parent.
7:04
So he has_kids and is not a smoker.
7:05
So, we have in this particular situation,
for her requirements, this profile here,
7:13
we have has_kids, that's true and
not is_smoker, so that's false.
7:19
So we have true and false,
that's a false, that didn't work out,
7:24
Heidi is gonna swipe left.
7:28
That's just isn't the one for here I
guess, here's hoping that she finds her.
7:30
Do you see the power of booleans?
7:34
They can help you to find true love.
7:36
Now, to really fall for booleans, I'd like
to show off the ability to run different
7:40
blocks of code based on their value.
7:44
This is called conditional branching.
7:46
Let's branch off to that topic,
right after this quick break.
7:48
You need to sign up for Treehouse in order to download course files.
Sign upYou need to sign up for Treehouse in order to set up Workspace
Sign up