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And let's now see what
are variables in Python.

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So here we have just
worked with numbers, okay?

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And you can see that,
so whenever we work with

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a number, if I want to
use number 3, okay?

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I just print 3, but then, well,
the 3 is just gone, okay?

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What if I want to keep a
value that I can use later?

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Well, I can use a variable.

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And to use a variable, it's very simple.

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You first have to give
a name to the variable.

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Let's name the first variable a and then
put an equal sign and then put a value.

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Let's put 3.

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So here, this statement,
this instruction, is

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basically put 3 inside
the variable named a.

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I press enter, okay?

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And here, nothing is printed.

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The instruction is just to put
the value inside the variable.

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Now, what I can do, I can
just write a and press enter.

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And now you can see a is evaluated to 3.

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And the good news is that now that I have
this variable, I can continue to use it.

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So whenever I'm going to call
a, I'm going to get the value 3.

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I can create another variable.

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Let's name it b.

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b is equal to, and I can also use some
computation that we have seen before.

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Let's say 4 times 2.

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Okay, and now if I get b, b is equal to 8.

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Okay, and if I get b
again, b is equal to 8.

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And a is still here, okay?

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So I can use a and I can use b.

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Now let's create another variable named c.

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And this time, what I'm going
to do is I'm going to create

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this variable from the
previous variables that we have.

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So a plus b.

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I press enter.

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And now what do we have in c?

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We have 11.

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Because at this time, a is going to be
evaluated to its value, which is here 3.

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b is going to be evaluated to 8.

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And so c is equal to 11.

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So you can create variables.

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And to do that, it's very simple.

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You put a name, equal, and then some value.

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You can add as many operations you want.

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And you can also create
variables from other variables.

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Now let's make a test.

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Let's say I change the value in a.

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Instead of 3, I'm going to put 5.

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Okay, and now let's see what we get in c.

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As you can see, c is still 11, okay?

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The variable a has changed
to 5, but c is still 11, okay?

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Why is that?

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Because simply when we assigned a value
to c, we evaluated a at this point, okay?

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At this time.

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And that's it.

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If you change a afterwards,
c is not going to be changed.

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Okay, so the order of the operation,
as you can see, is very important.

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Because now if I do c is equal to a
plus b, c will be equal to 13, okay?

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Because I'm evaluating
c, I'm assigning a

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new value to c after I
have modified a, okay?

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So here a was equal to 3.

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Here a is equal to 5.

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Okay, so a variable,
you can modify a variable

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during the program,
during the execution.

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So there is a notion also of time, okay?

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The variable can have
different values over

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time, depending on if
you modify it, of course.

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Okay, one other thing
I want to show you is if

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I, let's say I try to get
a upper case like this.

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You can see we have an error, name
error, name a is not defined, okay?

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Because you have to respect the case, okay?

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a, b, c.

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We have defined three variables.

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If I try to just, let's say test, okay?

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If I try to get any other name for any
other variable, I'm going to get an error.

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So make sure that you use the exact same
name of a variable, okay, when you call it.

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And then one last
thing for variable is that,

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okay, we use a, b, and
c for names for now.

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So this is nice, and this
is good when we want

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to make some tests or
some very simple program.

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But in the future, when
we write real programs, we

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are going to use meaningful
names for the variables.

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This is kind of your
first best practice, and

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this is maybe one of
the most important ones.

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So let's say you want to store here,
we just use a, b, c for just numbers.

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Now let's say you want
to store a temperature.

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So if you want to store
a temperature, you're

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going to write, for
example, temperature.

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That will be the name of the
variable is equal to, and let's say, 25.

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So now you have a temperature
variable, temperature 25.

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If you want to store
the age of the user, well,

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maybe you can just write user
age is equal to, and let's say 45.

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And then user age 45.

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Note that, so this is a convention
I'm going to use, okay, with Python,

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is when you want to use different words
for one variable, so this is possible,

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to separate the words, you are simply
going to use an underscore like this, okay.

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You don't use any uppercase letter, just
underscore between any word of a variable.

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All right, so to recap, a
variable is a container that

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you can use to store a value
and reduce that value later.

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To create a variable, you must first give
it a name and then assign a value to it.