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

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here we have just worked with numbers, okay? And

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you can see that so whenever we work with a number

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if I want to use number 3, okay, I just print

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3, but then well, the 3 is just gone.

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Okay? What if I want to keep a value that I can

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use later. Well I can use a variable, and to use a

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variable, it's very simple, you first have to give

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a name to the variable, let's name the first

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variable a, and then put an equal sign, and then

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put a value, let's put 3. So here, this

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statement, this instruction is basically, but

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three inside the variable named a, I press enter,

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okay, and here, nothing is printed. The

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instruction is just to put the value inside the

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variable. Now what I can do, I can just write a and

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press enter, and now you can see a is evaluated to

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3. And the good news is that now that I have

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this variable, I can continue to use it. So

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whenever I'm going to call a, I'm going to get the

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value 3, again, create another variable, let's

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name it b, b is equal to and I can also use some

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computation that we have seen before, let's say

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four times two. Okay, and now if I get b, b is

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equal to eight. If I get b again, b is equal to

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eight, and a is still here. Okay, so I can use a

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and I can use b. Now let's create another variable

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named c, and this time, what I'm going to do is

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I'm going to create this variable from the

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previous variables that we have. So a plus b, I

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press enter, and now what do we have in c, we have

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11. Because at this time, a is going to be

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evaluated to its value, which is here, three, b is

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going to be evaluated to eight, and so c is equal

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to 11. So you can create variables. And to do

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that, it's very simple. You put a name equal, and

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then some value, you can add as many operations

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you want. And you can also create variables from

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other variables. Now let's make a test. Let's say

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I change the value in a, instead of three, I'm

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going to put five. OK, and now let's see what we

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get in c. As you can see, c is still 11. Okay, the

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variable c has changed to five, but c is still 11.

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Okay, why is that? Because simply when we assign a

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value to c, we evaluated a at this point, okay, at

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this time, and that's it. If you change a

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afterwards, c is not going to be changed. Okay, so

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the other of the operation, as you can see is very

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important. Because now if I do c is equal to a

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plus b, c will be equal to 30. Okay, because I'm

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evaluating c and assigning the new value to c

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after I have modified a, okay, so here, a was

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equal to three, here, c is equal to five, okay, so

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variable, you can modify a variable during the

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program during the execution. So there is a notion

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also of time, okay? The variable can have

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different values of a time, depending on if you

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modify it, of course. Okay, one other thing I want

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to show you is, if I, let's say, I try to get a

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case like this, you can see we have an error, NameError:

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name A is not defined, okay? Because you

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have to respect the case, okay, a, b, c, we have

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defined three variables. If I tried to just let's

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say test, okay, if I tried to get any other name

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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

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the variable, okay, when you call it. And then one last

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thing for variable is that, okay, we use a, b, and

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c for names for now. So this is nice. And this is

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good when we want to make some tests or some very

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simple program. But in the future, when we write

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real programs, we are going to use meaningful

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names for the variables. This is kind of your first best

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practice, and this is maybe one of the most

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important ones. So let's say you want to store

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here, we just use a, b, c for just numbers. Now let's

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say you want to store a temperature. So if you

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want to store temperature, you're going to write

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for example, temperature. That will be the name of

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the variable is equal to and let's say 25.

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So now you have the temperature variable, temperature

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25. 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

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and let's say 45. And then user_age, 45. Note that

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so this is a convention I'm going to use okay with

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Python is when you want to use different words

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for one variable, so this is possible to separate

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the words, you're simply going to use an

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underscore like this. Okay? You don't use any

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uppercase letter, just underscore between any word

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of a variable. Alright, so to recap, a variable is

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a container that you can use to store value, and

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reuse that value later. To create a variable, you

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must first give it a name and then assign a value to it.