Python #25 - Logical Operators [By Mosh Hamedani]

[MUSIC PLAYING]

MOSH HAMEDANI: In Python,
just like the other languages,

we have three logical operators.

We have the logical and,
the logical or, and not.

Let's take a look
at a few examples.

So I'm going to start by
defining a variable name,

setting it to Mosh.

Now, let's say this is the
input that we get from the user.

We want to check to see if
name is an empty string.

How do we do that?

Well, earlier I talked about
the falsy values in Python.

So we have 0, empty string,
none, and an empty list.

These are all considered falsy.

So let's talk about
an empty string.

If this is interpreted
as false, then

if we apply the not operator
on it, we will get true, right?

So to check to see if
name is an empty string,

we can simply write a statement
like this, if not name colon.

That's it.

Print Name is empty.

Now, let's run this program.

Obviously, we don't
get that message.

However, if I change
this to an empty string

and rerun the program,
we get Name is empty.

But what if I add
a whitespace here?

Well, whitespace is
not considered truthy

because it's not
an empty string.

So, look, if I run the program,
we don't get the message.

To fix this issue, we can simply
call .strip method to get rid

of all the whitespace.

Now, let's run it one more time.

Beautiful.

So this is our not operator.

Let's take a look at
an example of and.

So I'm going to set age to 22.

Now let's see if age is
greater than or equal to 18

and age is less than 65.

We say you are eligible.

Good.

Pretty easy, right?

Now, here's a question.

How do we write that
expression in math?

We write it like this.

Well, more accurately, we
should add the equal sign here.

So age is between
18 and 65, right?

Well, I have good news for you.

In Python, you can simply
write this expression.

That's perfectly fine.

This is what we call chaining
comparison operators.

So we can rewrite this
expression in a simpler

and more meaningful way.

This is one of the
reasons that Python

is a highly popular language,
because the syntax is

so clean, without any clutter.

It's easy to
understand, and it comes

with all these best
practices and standards

for writing clean code.

So let's rewrite this
to 18, like this.

Good.

Now, let's run the program.

Obviously, this
person is eligible.