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Hi, welcome back!

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In the previous video we wrote, this simple program which returns the number of hours in a week.

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Now let's get a bit more real and improve this program by making it more readable, because the problem

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now is that let's say you wrote this program, but then you come a week after and you open up, you

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see the code and you don't remember what this is about.

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It just says 24 times 7.

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So, I mean, what does it calculate?

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Well, variables will save your day.

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So let us improve this program by using variables.

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I'm going to rename this using rename to basics_old.

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And create a new file and say basics.py.

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And what you can do is you can right-click over this tab, basics_old.py, and you can split

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it right.

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So now you can see both the new file and the old file just for reference.

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So we want to make a program that calculates the number of hours in a week.

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How many hours in a day?

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24.

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So how about saying day_hours equal to 24?

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And week_days equal to seven, so what I just did is I created two variables day_hours and week_days,

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so that allows me to understand what these numbers are and variables will provide that sort of feature.

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And so a variable basically is a name you give to an object.

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So these are that are two objects.

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In this case, they both happen to be number objects or more specifically integers.

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But we are going to cover all types of objects later on.

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And there's also other types of objects such as strings and lists and tuples.

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You're going to learn everything.

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But for now, it's important to know that variables are names attached to an object and to write variables

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you can write,

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you can choose whatever name you like.

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So I like to call it day_hours with an underscore.
Note that you cannot have spaces in variables.

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So that is not allowed.

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You will get an error.

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So if you want to have variables with two names, you want to use an underscore between the names.

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Day underscore hours. This is optional, so you can have a space here or not.

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But by having spaces around the assignment operator make the code more readable. Either way it will work.

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But this is more readable. In variable names

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you can use numbers so you could say day_hours1.
That would be fine, but it's not fine to start the

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variable name with a number such as that.

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You see, it becomes red, the python extension is highlighting it to red.

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Actually if we run it you'll get an error.

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You see that green button here?

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It says that syntax error, invalid syntax, so you cannot start the variable name with a number.

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Delete that, run again using that green button.

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And in this case, we didn't get an error.

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However, we didn't get an output either.

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Why?

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Well, because we are not printing out anything.

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So if you want to see output in the terminal, you want to use a print function.

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In this case it would be (day_hours * week_days).

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Now, just something I want to tell you is that if you execute this using the other way, such as

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Python3.9 basics.py...

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Sorry, that is the command for Mac, I'm on Windows, so I'll do py -3.9 

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basics.py.

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So the program was executed.

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We didn't get an error, but we didn't get an output either.

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That is because when you use this command, the script, the file is not saved automatically.

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So basically what I just did here is I executed the previous version of the script, which was without

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this line.

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So I didn't save the scripts and this command is executing the previous version of the program.

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So if you are using the command line commands like that and not that button, you want to first save

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the file with File, Save or Control S, the shortcut, whatever you like, then I can use the upper

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arrow key to call the previously executed command and then presenter to execute.

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And this time we get 168.

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So the output that we were expecting is the same output that we get with this green icon.

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So you can see that just like we did multiply the numbers so we can also multiply variables.

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So a variable is the representation of an object.

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When you are doing operations with variables, you are doing operations with the objects referred by

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those variables.

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Of course, we can improve this even more by saying week_hours.

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So a new variable which should be equal to day_hours times week_days, and then in here

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we say week_hours to print the week_hours, execute and we get again 168.

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See that here I used an empty line, Python will ignore this line so it doesn't matter how many blank

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lines you have in your code.

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These are just for readability, for your own convenience

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as a programmer. A blank line would make also sense in here.

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They allow you to group certain parts of your code.

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So here we are creating the input variables.

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And this here is a formula

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that calculates the output, and then here we return that output.

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So what happened here is that a new object was created, so 168, and that object was stored in that variable.

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So it's being referred by that variable.

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The variable now represents 168 and then we print out the value of that variable.

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So the object of the variable, that prints out 168.

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So even if this is longer than this,

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it is much better because first it is more readable.

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And second, it also allows us to expand the program.

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And that was the lecture about the variables, so two key points to take from this lecture.

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First, variables will make your code readable.

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And second, variables are used as transporters.

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So they transport objects from one place to the other.

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For example, in our example, we stored an object in this variable through that formula.

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So 168 is being referred by week_hours, and week_hours transports for that 168 number to the print function,

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so the print function prints it out.

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And that is about variables.

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Thanks a lot for following!

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I'll talk to you later.