Hey everyone, Kevin here.
Today I want to show you the fundamentals of programming using Python.
In this video, I'm going to assume that you have no programming background at all.
We're going to start from the very basics and we're going to work our way up step-by-step,
and we'll get a little bit more advanced. By the end of this video,
you'll be able to write your very own source code and then run it.
Now, how exciting is that?
We're going to start with, well, why should you even learn how to program and then why Python?
There are so many different programming languages out there.
Why should we choose Python? Then we're going to start with how do you even get Python?
Where do you write your code?
Then we'll go through things like operators, variables,
we'll create a function, we'll even jump into things like creating an if statement,
creating loops, so your code will run or execute until a certain condition is met.
We'll even leverage others’ code by importing libraries into Python.
By the end of this, you'll have a very solid understanding of how to get started with
programming. Think of this as a 100-level course that'll give you all of the most essential tools.
If you want to jump around this video, I've included timestamps down below
so you can jump to the section that interests you the most.
To get started, you might be wondering, well, why should I even learn how to program?
How is this going to benefit me?
Well, anytime you go on your phone or anytime you go on your PC,
you're experiencing the output of something that someone has programmed.
So, you're realizing the benefit.
Think of it this way. To program allows you to take maybe an idea that's in your head,
you can turn it into a series of steps that the computer can understand and execute.
How cool is that?
So, for example, maybe you have a game that you want to create.
Maybe you want to create an application at work to help simplify what you do on a daily basis.
By programming, you can do all of those things.
It's an incredibly powerful skill to learn how to use.
OK, so you want to learn how to program, but why Python?
There are so many different programming languages out there, you have C, C Sharp,
C++, Java, JavaScript, PHP, and the list goes on and on.
Well, recently on my YouTube channel, I asked all of you what programming language do you
most want to learn about? And overwhelmingly, far and away, Python was the clear winner.
It was something like 65% of you wanted Python. And it kind of makes sense. When you
look at the lists of the most popular programming languages, Python tends to be right near the top.
It's been around for a while.
It's also pretty easy to use and also understand.
When you code using Python, it tends to be a very concise programming language.
It's also a good general purpose programming language,
and what I mean by that, is you can write all sorts of applications.
Maybe you want to write a web app, an internal company tool,
a game, or maybe you just want to conduct some scientific analysis.
You can do all of that with Python.
And all the things that you learn today related to Python,
you can take these same concepts and you can apply it to other programming languages as well.
And really, fundamentally, you just want to take some idea you have,
you want to turn it into a series of steps that the computer can execute.
And in a sense, it's kind of like a different language or a spoken language.
So, in English I say hello, in German I'll say hallo,
and in French, I'll try my best, I'll say bonjour.
And all of those communicate the same idea. I'm just saying hello, but it's a slightly
different way of saying it or speaking it, and that's the same with a programming language.
They have different syntaxes. They also have different rules,
but at the end of the day, you're simply trying to communicate something to the computer,
because you want the computer to do something for you. Now of course, each programming language
might have its strengths or weaknesses, but you're really accomplishing the same objective.
All right, so why don't we jump on the PC and let's get started with Python.
Here I am now on my PC and first off I want to check if I already have Python installed.
To do that on Windows 10, simply go down to your
taskbar and within the search field type in command prompt.
Once you type in command prompt, click on the best match.
This opens up your command prompt, and to check for Python,
simply type in Python and then type in --version.
If you have Python installed, it'll tell you the version of Python that you have, and here you see,
I just typed this in and it says Python was not found, so I need to go and install Python.
If you already have it, you can skip the next step. If you don't have Python like me,
stick around and I'll show you how you can get Python.
To get Python, head to the website python.org and that'll drop you on the Python home page.
Right near the top, you'll see a button right here for downloads.
If you click on this, it'll identify what operating system you're on
and it'll recommend the best option.
However, if you're on a different OS, you can also choose it down here. Now I'm running
Windows today, so I'll download Python 3.9.2. This is currently the most recent version. If
you're watching this video maybe a few months from now, there could be an even more recent version.
Go ahead and download whichever one it recommends to you.
I'll click on download and here it's kicked off the download process.
Once you finish downloading, click on the EXE.
This opens up the install prompt and right up here I could install.
However, before we do that,
there’s an option right here at the bottom that says add Python to PATH.
Let's check that box and then click on install now.
This now runs through the installation process, and it looks like the setup
was successful, so I'm going to click on close.
Let's now go down below and just like we did before, you can type in command prompt
and then launch the command prompt. Once again, we can type in Python
–version, hit enter, and you should now see that Python is installed. Here I have Python 3.9.2.
OK, now that we've verified that Python is successfully installed, let's close command
prompt and once again, let's go down to the taskbar, except this time let's type in Python.
And here you should see the best match for Python. Here I see Python 3.9. Let's click on this.
This opens up the Python terminal, and I'll zoom in just a little bit, so it's a little
bit easier to see, and we can type in code directly here and Python will interpret it.
So, what's an example of that?
So, what if we type in what is 1 + 2 and I'll put a question mark in and let's hit enter.
And this doesn't work.
I see something that says syntax error, invalid syntax.
Now the syntax is the rules of a programming language and when I typed in what is 1 + 2?
This doesn't align with what Python is expecting.
I need to type in a valid expression that the Python programming language understands.
So, instead of typing in what is 1 + 2, well I could just type in 1
and I'll type in + 2, and then I'll hit enter and there gives me 3 back,
so this was a valid expression in the Python programming language.
Now, what's neat is when I type something into Python, like 1 + 2, Python takes each
line of code that I enter. So the 1 + 2, it interprets it, and then it evaluates it.
So, it gave me 3.
There are other programming languages where you have to compile it first
and then you can execute it, but with Python it'll interpret it as you’re going to.
Now, now that we've typed in just a very basic expression, and we've evaluated it,
why don't we try a built-in function called print. Here I could type in print,
I'm going to open the parentheses, insert double quotes, and then I'll type in Hello World,
and I'll close my quotes and close my parentheses.
Now this is one of the go to examples anytime you're starting with a new programming language.
It's just hello world. Just testing it out.
I'll hit enter and here it says Hello World, so it's sending back exactly what we sent into this
function. Now as we go throughout this, our programs are going to get a little bit more
complex, but this is just showing you the basics of how you can already start executing some code.
To exit out of the Python terminal, we can click on the X symbol up here
or we can type in another function called exit.
Open your parentheses, close your parentheses,
then hit enter and that'll close out the terminal window.
Now we executed some of our first code directly in the Python terminal, but you can also use
a text editor to write code. On Windows, there's a text editor called Notepad.
Once again, go down to your taskbar and in the search field type in Notepad.
I'll click on this right here.
This opens up Notepad, and I'll zoom in just a little bit more. Now you probably
never knew that you can write source code in Notepad.
It's actually a pretty powerful app. So right here, just like we did in the previous example,
I'll type in print and then I'll open my parentheses, put in a quote, and then
I'll type in Hello World once again, and then I'll close my quotes and close my parentheses.
So, here's my source code written in Notepad.
Now of course I want to be able to run this, so I need to save it as an appropriate file type.
I'll go up to the file menu, go down to save as, and this opens up the save as prompt.
Now maybe I'll just call this file, let's call it Hello World, and if I just leave it as that,
it'll save it as a .txt or basically just a standard text document.
Now I want this to be a Python file and it turns out that the extension for Python is .py,
just like the extension for text files .txt, Python is .py, so here I'll type in .py.
Depending on the programming language that you're using,
different programming languages have different extensions.
For example, JavaScript is .js and every language will have its own extension.
Now that I've typed this in, I'll save it to my desktop and then click on save.
And here now I see the file on my desktop called Hello World.
You'll also notice that it has the Python logo on it. Because we installed Python,
it correctly identifies that this is a .py file and so it sees that this is a Python file.
Now let's test this out to see if we can run this source code that we wrote.
Down below on the taskbar, let's type in command prompt,
just like we did earlier, and let's open up the command prompt.
I've adjusted the command prompt so it's a little bit easier to see,
and now I want to run this file over here in command prompt.
To do that, let me type in Python.
So, this will let the computer know that this is a Python file that I want to run.
I'll put in a space, and I'll take my Python file,
and then I'll simply drag and drop it over into command prompt.
Now this is a really cool trick
where you can get the location of the file simply by dragging and dropping it in.
So here basically I'm saying I want to execute this Python file.
Next, I'll click on enter and here we see that it prints hello world into my command prompt.
This is exactly what I wanted it to do, so Python went through,
and it interpreted the code in this file and then it printed it here on my screen.
You now know some of the basics of both writing and running Python code.
Congratulations, you just wrote your first bit of source code, and you also ran it.
You're making some good progress.
Now, so far, we've just been writing our code in a text editor like Notepad,
and then we've been running it, and that works perfectly fine,
but it's not the most efficient way to write code, and I just want to give a parallel example.
Let's say that maybe you're writing a document for school.
You could write your document in Notepad. Now of course it does have some downsides.
You don't have a spell check.
You don't have a grammar check. You can't do formatting.
So, although you can do it, it's going to require a lot more work.
And that same concept also applies to programming.
Sure, you could write your code in Notepad, or we can get what's called an IDE,
and that stands for integrated development environment.
It'll just make writing code a lot more efficient and also easy,
and in a few moments, we'll see why that is.
You have all sorts of IDEs that you can choose from.
On Apple, you have Xcode. On Android, you have Android Studio. With Ruby, you have RubyMine,
and there's also another one called Visual Studio Code and that works very well with Python.
It's a product made by Microsoft, so of course I like it. I used to work at Microsoft,
but the great thing too is Visual Studio Code is entirely free,
so let's go to Visual Studio Code and let's get this IDE.
To get Visual Studio Code, head to the website code.visualstudio.com
and once you land on the homepage, you can choose the operating system that you have.
Here when I click on the drop down, you can get it on Mac,
Windows, or Linux, so it supports all of the different major operating systems.
I'm running Windows today,
so I'll click on download for Windows and I'll go with the stable build.
Once the download completes, down in the bottom left-hand corner, click on the EXE.
This opens up the setup process.
I’ll agree, I'll Click to accept the agreement and then click on next.
I'll go with the default location.
I'll click on next.
You'll then get a screen that says select additional tasks.
I’d recommend checking all of these different boxes.
Next, let's go down and click on next. On the last screen, let's click on install.
This will now go through and install Visual Studio Code on your computer.
Once you're all done installing, let's click on finish and launch Visual Studio Code.
This now drops us into Visual Studio Code, and by default, we'll land on the welcome screen.
If you ever want to get back to this screen again,
you can click on the help menu and then click on welcome and that'll drop you right here.
There are a few things we want to do before we can start writing code in Visual Studio Code.
Over on the left-hand side, there's an icon here for extensions.
Let's click on that.
This opens up extensions and up here in the search field type in
Python. We want to install the Python extension.
When you type it in, you should see Python at the very top,
and when you click on this, you'll see that it's Python by Microsoft.
It should have something over 30 million downloads,
and right here, if you don't yet have it, you can install this extension.
We're going to need this, so click on install and make sure you add It. Once
you finish installing the extension, we also want to select Python that we just
installed as the interpreter for Visual Studio code, and this is really easy to do.
On your keyboard, press control, shift, and P at the same time, so that's control, shift, and P,
and that'll open up this screen right here and up here, type in Python: select interpreter.
This will allow us to select the interpreter that we want to use.
Now if you remember in Notepad, when we wrote our code, it interprets that code.
So, we basically want to tell Visual Studio code what interpreter we want to use.
So, I'll select this option right here
and now I can choose my interpreter, and here you'll see Python 3.9.2.
So, this is what we installed just a moment ago.
So here I'll select this as my interpreter,
and now we're all set to start writing code in Visual Studio Code.
To get started, why don't we open up the Hello World file that we created previously.
Here I'll go up to the file menu and I'll go to open file.
This opens up my file picker and here on my desktop I see my hello world file.
Here you'll also see that this type of file is now associated with Visual Studio Code.
This is the Visual Studio Code logo.
I'll select this file and then click on open.
Now that I've opened the file, you should recognize this.
This is exactly what we wrote into Notepad,
except this time we have it open in Visual Studio Code. Now you'll start to notice
some of the benefits of using an IDE or an integrated development environment.
First off, I have line numbers now, so here if I add additional lines of code,
here I get all the line numbers over on the left-hand side.
In Notepad, we didn't get that.
Also when I write in this function called print, it highlights it in different colors
so I could identify what is the context or the text that it's printing and what is the function.
So here I get different colors.
Also, when I hover over print, it gives me some helpful suggestions
on the type of content that I can enter within this function.
So, this will make it a lot easier as we start writing out our code.
Now I can run this code directly in Visual Studio Code.
I'll simply go up here and I can now right click.
Right down here, there's an option that says run Python file in terminal.
When I select that, it'll open up a terminal on the bottom of the screen,
and here I can see that it executed or interpreted this file and here it prints out hello world.
So, it gives me the output of this code right up here.
Along with right clicking on the screen and running the Python file in the terminal there,
I can also go to the top right-hand corner and I can click on this play icon.
This will also run the Python file in the terminal, so when I click on this,
here too, it ran this file and here too I see hello world.
So, this is just another way, probably a little bit easier to see the output of your code.
Now that we know some of the basics of how to start writing code and how to run that code,
I want to show you how we can start working with operators to work with numbers.
And here I'm going to type directly into the terminal down below, so I'll go down here to
the terminal and just like we did earlier in the Python terminal, I can type in here.
So here I'll type in 1 + 2
and I'll hit enter and here it interprets that code, and it evaluates it to 3.
So just like we saw earlier. One of the things is you'll notice when I typed in 1 + 2,
I didn't include any spaces and spaces or whitespace don't impact the calculation at all,
so I could also type in 1, space, and I'll type in plus, and then another space, and hit 2,
and then hit enter and there too it also evaluates it to 3, so using white space can actually make
your code more readable, so you could type it in like this, or just include some white space.
It won't affect what the outcome is. With Python, I can use all of the standard
operators. Right up above, I showed you how you can do addition, but here let's say 5 – 2,
I can also do subtraction, and here it evaluates that to 3 as well.
I could do a multiplication, so let's say 4 * 4.
Now with multiplication, I enter in an asterisk.
That's the multiplication symbol.
Here I'll hit enter and it evaluates that to 16. I could also do division. Here I'll take 10 / 5 and
here for division, division is the forward slash, and then I'll hit enter and that evaluates to 2.
Now with Python, let's say that you start using multiple operators,
so maybe you're adding and then you're multiplying.
Python follows the default order of operations,
so let's say I enter in 2 + 2 and then I want to multiply by 5.
What do you think this will evaluate to?
Is it 2 + 2 which is 4 and then times 5 which is 20?
Or is it 2 * 5 which is 10, and then you add 2 to that which is 12.
Well here if I hit enter, it evaluates to 12,
because it's following the default order of operations. Multiplication comes before addition.
If you've ever heard PEMDAS or Please Excuse My Dear Aunt Sally before, that's how you
know what the order of operations is. First it'll evaluate whatever is in parentheses.
Then it'll look at any exponents followed by multiplication and division in the order of left
to right, and then it'll look at addition and subtraction also in the order of left to right.
Up above, I could also enter in my expression up here,
so here I'll get rid of hello world and here I'll say let's print out 2 + 2.
Here I'll click on run and here you'll see that it executes this
code Thanks for the suggestion! I’ve added this to my list. Stay tuned. Cheers!and here this also
evaluates to 4. If I want to use an exponent, I'll come up here. Let's remove the plus symbol,
and here I'll enter 2 asterisks, so this will be 2 to the power of 2.
And here if I click on the play button, here that evaluates to four 2 * 2 is 4.
But let's say I want to do a 2 to the 3rd.
Here I'll evaluate and it comes out to 8. I also have access to the floor operator,
so let's take an example here. Let's say I want to calculate 5 / 2, and here I'll play
and right down here I see that's 2.5, so I have a remainder of .5.
But let's say I don't want to know what the remainder is.
I just want to know how many times it goes in without a remainder.
This is also known as the floor.
I could insert another forward slash and then I could run it and here it tells me that it’s 2.
But let's say I just want to know what the remainder is,
I can use the modulus operator for that.
I'll get rid of the forward slashes, and right here, I'll type in the percent symbol,
then I'll hit go and here it tells me that the remainder is 1.
As I'm entering in numbers up above and as I'm working with numbers,
let's say that I enter a very large number. So, let's say I enter in maybe 1,000,000.
Now I could go through here and I could enter a comma and then I'll type in the zeros
and if I hit go here, you'll notice that it doesn't print what I expect it to.
That's because we don't want to use commas as we're entering numbers.
Instead, when you enter a number,
just enter it in as is and then hit go, and here it prints exactly what we expect.
So, you don't want to use commas when you're entering in numbers.
Now that we've entered in some numbers, and we know a little bit about the basics of
how you can work with numbers and operators,
let's start working with some text or what's referred to as strings.
Let's say that I want to print what's up. Now earlier, we printed out hello world
and it's the same concept here. I'll insert in double quotes and then I'll type in what's up.
So, here's what's up and I'll click on this play
icon and down below you'll see that the output is what's up.
Now I surrounded what's up with double quotes. Now instead of using double quotes,
I can also use single quotes up here.
So, if I enter in single quotes and then hit play, here too, you'll see that I get the same output,
so I can choose whether I want to use double quotes or single quotes.
So why would I want to use one versus the other? Well,
here, what's up should actually have a single quote, so I'll insert a single quote there.
Now one of the problems is when I enter a single quote here, it thinks that this
is the end of the string, and so now if I try to run it, I get a syntax error down below.
So instead, I can use double quotes here and I'll use double quotes at the end,
and I could use a single quote in the middle and then here I'll run it and it works properly.
Now let's say you wanted to use double quotes within your text.
Well, you could surround it with single quotes and that way the double quotes would show up.
Now here too, just like we saw before, whitespace doesn't impact how the code runs,
so if I want to insert a space here and maybe insert a space there and another space here
and I run this code, here you'll see that I get the exact same output.
So once again, by using white space,
that can help make your code more readable as you're going through.
We now know some of the basics of working with numbers and also strings,
but what if you want to make sure you explain what's happening in your code?
How do we do that?
Well, we can use something called a comment, so let's say that I have this code here and I
want to explain to someone what this does. Here I’ll bring this code down to the second line and
I can insert a comment by entering in the hash symbol or the number sign or the pound symbol,
so I'll enter that and here I can say this prints some text.
I've now typed in my comment and let's run this now
and here you'll see that this doesn't affect at all what appears down here.
I simply get what's up.
So just like we got before. Now I could also take a comment and I could put it on a line with code.
So here I'll put it after my code,
I'll hit run, and here too you see that it just gives me what's up.
Now one of the neat things is,
let's say I start writing a lot of code and it's starting to get fairly complex.
I can comment out a line of code.
I'll put the hash symbol in front of my code and here you see it turns green,
so this is the IDE’s way of telling me that this is a comment.
And here now, if I hit run, you'll see that I get no output. That's because I commented out
this line of code, so here I could bring it back by removing it and now here if I run it
once again it shows me what’s up. So comments are pretty valuable as you're writing code.
Not only to let other people know what's happening in your code and what different blocks of code do,
but you can also use it when you're troubleshooting to
cancel out certain areas of your code until you're ready to test them again.
Next, we're going to look at how you can use variables,
and the easiest way to explain a variable is to use this red bucket that I have here from my son.
So, let's pretend that this red bucket here is a variable and we can name the variable.
Why don't we just call it red bucket, just to keep things simple.
Now I can assign a value to this variable, so let's take for instance.
Let's say I want the red bucket to equal my name Kevin.
So here I have my name.
I can take this value and I can assign it to this variable.
So now if you say well, what is the red bucket, well,
right here the red bucket is currently Kevin.
So once again, I've assigned that value to it.
And this is a string or basically my name is referred to as a string.
It's just a set of characters.
Now I could assign other types of data to this variable as well, so maybe I say, well,
actually I want the red bucket now to equal a number, so maybe I want it to equal #8.
So, I'm going to say red bucket, you're now equal to 8, so I'm going to take my name.
We're going to pull that out, and here I'll take the number 8 and we'll put it in the bucket.
So now if you ask me, well what is the red bucket?
Well, it's currently the number 8.
That's a general concept of a variable.
The variable can hold different values.
Let's jump in now and see how we can use variables. To create variables,
there are some rules that we need to follow, or this is the syntax that Python looks for.
A variable should only contain letters, numbers or underscores.
And also, we just need to make sure that we don't start with a number.
We can't use any spaces in a variable name.
We also can't use any known keywords to Python like break or try.
And ideally, we want to make sure that a variable name is short and descriptive.
Those work best.
So, for example, with the red bucket, we'll now simply call the red bucket,
so it's pretty short and also descriptive.
Also, variable names are case sensitive, so if I wrote red bucket with a capital R and another
one with a lowercase r, Python would view those as separate variables, so case sensitivity matters.
OK, so let's create our first variable and just continuing the example,
let's say I want the variable to be called red bucket, so I'll give it this name
and now I need to assign a value to this variable, just like I did with the bucket. I'll type in
red_bucket and I'll type in the equal sign and I'm going to assign it the value of Kevin, my name.
And here I'm using just a single equals sign. So,
what this does is it will assign this value to this variable.
So now here I could hit enter and let me run this and here nothing shows up yet
because I've assigned this value to this variable.
The next thing we could do is actually print this out.
So here let me say print and let's type in red bucket.
What's nice is because I'm using an IDE, it recognizes that I
created a variable called red bucket and I can just click on it here.
Now if I click on the play icon, here it'll print out Kevin,
so it's printing out the value that's assigned to the red bucket.
Now let's take another example here, let's say I add another line and
let me copy this first line and I'll paste it into the second line.
And here I want to assign 10 to the red bucket.
So here I start out by assigning Kevin and then I assign 10.
What do you think will print out?
Let's click on the play icon and here it prints out 10.
And the reason why is, well, first it assigns Kevin to Red bucket,
and so that's the current value. But then on the next line of code, it assigns a 10
to the red bucket. So, the 10 overwrites Kevin, and then when I print out the red bucket,
it's taking the last value that was assigned to it. So, the way to think of this back to
the bucket example is I put Kevin in the bucket and then when I put 10 in, I have to take Kevin
out and then I put 10 in, so at the very end when you ask well what's in the red bucket,
well, the number 10 is the in the red bucket because that's the last item that I put in.
One thing that's really neat about Python is when you're defining your variables,
you don't have to assign your variable a type.
So here for example, for the red bucket, I assigned it my name,
and that's also known as a string.
And next I assigned a number, which is an integer, but I don't have to go and say,
well, the red bucket is a string or a red bucket is an integer,
it'll automatically know what data type that I'm assigning to that variable.
So down here in print, I can type in type
and then I'll open and close the parentheses around this variable.
And so now let's run this and here it's telling me that it's an integer.
So basically here 10 is assigned to red bucket,
and so it's telling me that that's currently an integer.
Let's get rid of this line right here.
So now Kevin will be assigned to Red Bucket.
And when I run this, here you'll see that a string data type is assigned to this variable.
Now let's say that I want to get rid of a variable,
so maybe I don't have a need for the red bucket anymore.
Down here I can type in del, basically delete and this will delete a variable,
and here I can type in red bucket again. I'll select the suggestion.
Let me get rid of the type in the print, so I just want to know what is red bucket? So if we run this
now, I'll get an error because it says red bucket is not defined and that makes sense because here I
created the variable, I assigned the value, here I deleted the variable, and here I try to print the
variable, but there is no variable anymore called red bucket because I deleted it right up above.
Next, I want to show you an example of how you can request
input and then you can take that input and assign it to a variable.
So right here I simply typed in Kevin and I assigned it to this red bucket,
but I want to allow input. So right up here, let's delete Kevin or delete your name that
you entered in and here we'll type in the input function. Here I'll open the parentheses and let
me type in double quotes and maybe I'll ask the question what do you want to put in the bucket.
I'll enter a question mark and then an additional space.
Now right down here, I don't want to delete the variable, so I'll get rid of this.
So right now, I'm going to ask for input and then we'll print out whatever the input is.
So here let's click on the run icon and this will run it.
Right down here it says what do you want to put in the bucket?
And so maybe I want to put a shovel in,
so I'll click down in the terminal, type in shovel, and then hit enter.
And here now it prints out shovel, because that's now the value of the red bucket variable.
Next, I want to show you how we can start using conditional logic in our code.
Basically, any expression that you enter in breaks down to either true or false,
so let's just take an example.
I'll go down a few lines and let me enter in print and I'm going to ask is 5 equal to 4?
One of the things you'll notice is when I ask this question is 5 equals to 4,
I entered in two equal signs and that's not a typo.
Up above, I just entered in one equal sign.
So why do I enter one here and down here I enter two?
Well up above, I'm taking this value or this input and I'm assigning it to this variable.
Here I want to run a test for equality.
I basically want to check are these two equal,
and when you test or check for equality, you use two equal signs,
so here let me remove the code up on top and I'm simply going to print out is 5 equal to 4.
Here when I run it, here we'll see that no, it's false.
5 does not equal 4.
Now you might be saying, well of course 5 isn't equal to 4.
It's not equal to, so over here I can also check are they not equal to one another.
So here instead of the equal sign, I'll insert an exclamation mark.
So here I have an exclamation mark followed by an equal sign.
So, this is my way of asking the computer is 5 not equal to 4?
And I think we all know that's true.
So, when I run it, here I get true back.
Along with equal to and not equal to, there are many other operators that I can also use.
I have less than, greater than, greater than or equal to, and less than or equal to.
And here you can see the symbol that you can use for these different operations
and over on the right-hand side, you'll see a few examples of how you could use this, so I could
insert any one of these into that print statement and you'll get this corresponding result.
We can now take these different operations and we can combine it with
variables that we just learned about and so let's type in an example here.
So, I have a young son at home. His name is Thomas and he's just three years old,
so let me create a variable and I'll call it Thomas age and it's currently equal to three,
so I'm taking this value of three and I'm assigning it to this variable.
Now let's say I want to check, well, is he old enough for kindergarten.
So maybe I type in age at and I'll type in kindergarten.
And maybe age at kindergarten is 5, so I'll enter in equals 5,
so I now have two different variables and I've assigned a value to each of those variables.
Now down here I can check the equality of these,
so maybe I'll say print and let's check is Thomas age, is that equivalent to the age at kindergarten
and so then I'll hit run and here we'll see that's false because basically Thomas age is
coming back as three, age at kindergarten is 5, and those don't equal one another.
So, we can do this same type of check except we could do it using variables.
Now with this expression here, I'm simply checking
is Thomas’ age equal to the age at kindergarten and it comes back as false.
But what if I want to do something a little bit more complex?
What if I want to check, well if Thomas is less than the age at kindergarten, well,
he should probably be in preschool or daycare. And if he is 5, he should be in kindergarten.
But if he's older than five, he should be in some other class.
And right now, this is just doing one check, it's just looking at one point,
is he at the age for kindergarten?
The easiest way to think of this is like a flow chart, so here I have the current
age and depending on his age, any one of these different scenarios could be true.
Now I won't be able to do that with the simple expression that we wrote.
That's just checking one thing.
If I want to check multiple different criteria, this is when I can use an if statement.
So, let's jump back into Visual Studio Code and let's look at how we can use this.
Back in Visual Studio, I'm going to delete this last line and I'll keep these two variables.
The one with Thomas' age and the other one with the age at kindergarten
and I'll enter down a few lines. Once again, the white space doesn't matter,
so don't worry, you could enter down a few lines and now we want to
enter in an if statement. An if statement is really easy to write, you simply type in if.
And here now I can do my check.
So first I want to know is Thomas’ age less than the age at kindergarten?
So here I can type in my variable.
Once again it gives me this helpful suggestion of using Thomas’ age and first I can check if
he's younger than the age at kindergarten, so let me enter in the age at kindergarten.
So, this is going to be my first check.
Once I finish entering in this statement, I need to enter in a colon.
And when I hit enter, this drops me down to the next line.
One thing you'll notice is it automatically indented the line.
What will happen is it will check this and if it turns out that Thomas’ age is less than the age
at kindergarten. In this case, Thomas is 3, the age of kindergarten is 5, so this would be true.
It's going to evaluate this code, so whatever code I enter in here,
it'll go through and it'll execute that.
So, let's test this out and let me type in print, so I'll enter in this function
and maybe we say something like Thomas should be in preschool.
Once I finish typing that in, I'll go to the end of this line and hit enter again.
Here you see that it continues to indent it.
So basically, I can type in additional code and whatever I type in in this indented space,
it'll go through and it'll execute all of this code.
Now I don't have anything else I want to run.
I simply want to print out this message.
Let's now test this out to see how it works.
I'll go up here and click on run and here we get the text that says Thomas should be in preschool.
Now let's say that maybe Thomas is 10 now.
So here Thomas’ age is 10 and that is not less than the age of kindergarten.
So, when I run, here I get nothing back because it evaluates this, and it comes back as false,
so it doesn't execute this code.
Now there's nothing else here, so it simply returns nothing.
Now let's say I want some fall back, so let's say if this is false, I want to say something else.
Down here I can use else, so it'll check this, and it'll check if this is true,
but if it turns out being false, then it'll fall back to else.
So here I'll enter an else, a colon, and here again it indents out.
So here I could say, well if this isn't true then execute this block of code.
So here maybe I'll insert another print function.
So let me type in print.
I'll open up the parentheses and let me type in Thomas should be in kindergarten or another class.
So, I've now typed in my else statement, so let's try running it to see what it will happen.
So, it'll check the first if statement,
that'll evaluates a false, and then it should fall back to else.
Let's test this out. So when I hit run, here it says Thomas should be
in kindergarten or another class, so this logic is working exactly as we expect it to.
Right now, I have two conditions here.
I basically checked the first condition and if this is false, it just falls back to this one.
But let's say I want to check for additional conditions.
Here I'll enter down and let me get out of this block of code, so I'll hit the backspace key,
and right here, I can enter something called elif, basically else if,
so, you can go through and check any number of conditions.
It'll start at the top and when it finds one that's true,
it'll display that message and then exit.
But if this is false, it'll go to the next one and check that condition,
and I can add any number of else ifs in here.
So I'll type in elif and maybe for this condition I want to know if Thomas is 5,
well he should be in kindergarten.
So here I'll say Thomas age and here once again,
I want to check if it's equal to the age at kindergarten.
And remember, we don't enter in one equal sign,
we enter in two and here I'll enter in the other variable age at kindergarten.
So, this is going to be my check.
And if this is true, we now want to evaluate some code. Now just like we did before where
I entered the colon, let's make sure we enter in a colon here at the end.
That's part of Python syntax.
I'll hit enter and this automatically indents me.
Here I'll type in print, and I'll type in some text that says enjoy kindergarten.
Now I've added this else if statement that checks to see if he's in kindergarten.
So, this last statement no longer makes sense where I say Thomas should be in kindergarten or
another class, so maybe I simply remove this and I say Thomas should be in another class,
so this will just be my catch all at the end.
So, let's test this out to see how it works.
So, let's say Thomas is 3 and I run it.
In this case, the first condition here is true.
So, Thomas should be in preschool and here I get the text down below.
Thomas should be in preschool.
Now let's say Thomas is equal to five, or maybe he's five years old now.
When we run it, here the first condition is false, so it skips over that one.
It looks at the second condition,
this elif, and here Thomas is 5 and that's the age at kindergarten.
So here I get the text saying enjoy kindergarten.
And let's say now that maybe Thomas is 10.
So here when I run it, it evaluates the first statement and, well,
he's older than the age of kindergarten, so that's false.
His age is not equal to the age of kindergarten, so that's also false,
and then it falls back to the else statement, and so Thomas should be in another class.
So here we've just tested that this is working just like we expect it to.
Next, I want to show you how we can use functions in Python and if you've ever
used any other programming language before, you might know them as a subroutine or a method,
but it's all the same thing, so we're going to use functions.
And you've actually already been using a function.
We used the print function. Right here you see that we've been using print multiple times.
This is a function. You call this function, you pass in some text,
and then it prints it out on the screen.
So that's just a basic example of a function that we've already been using.
Now the cool thing is we can create our own function.
So, what is a function?
Well, it's basically a block of code
that you can package together with a name and it does something.
So, in this case anytime you call print or input, it takes some action depending
on what that function is. The neat thing is it makes your code more modular and also reusable.
So here for example, every time we want to print something on the screen,
we simply call this function and then it takes that action.
We don't have to enter in all the different code associated with printing your text on the screen.
We simply rely on this function.
So, it makes your code a lot more reuseable.
So let's go through and create our own function.
Right now, I'll go through and delete all of this code that we had and let's say just to show the
value of functions, let me just enter in print and then Kevin Stratvert has a great channel.
I'm going to enter this in three times.
I figure the more I say it maybe the more it sticks,
then the more you read it, you might start to believe it.
So here I've typed it in three different times and now I'm going to run it.
Here I'll expand the terminal just so we could see it and here printed out three times.
Oh, but actually, look at that.
It looks like I spelled Stratvert wrong. Stratvert has a T in the middle,
and here I just say Stravord. Now because I'm not using a function for this, well,
I'm using the print function, but I haven't created a function to print this out three times,
so I'd have to go through, and I'd have to correct every single Stravert throughout my code
to correct this and imagine that you referenced something many,
many, many times in your code, and maybe you make an error, you need to update something.
It could be a pain to have to go through all of your code to update it.
So instead, you can create a function, and I'll show you how we can create a function
to print this out multiple times, and then we can call it whenever we want.
OK, so let's create a function.
I'll simply go down a few lines.
To create a function, we have to type in def.
This basically stands for define, so I'll type in def and here we can type in a name
for our function, and I'm going to call this function, let's say print Kevin.
So, I've typed in my function name and then all functions need to have parentheses at the end, so
I'll open the parentheses, close the parentheses, and write down here, once again, just like we did
with the if statement, I'll insert a colon. So, I now have my function. When I hit the enter key,
here too, just like with the if statement, you see that it indents it automatically.
So once again, it indents and any of the code underneath here will be part of this function.
Next, I want to enter in some code in this function, so maybe I'll set up
a variable and I'll call this text and let me insert some text here in quotes,
and maybe I'll say Kevin Stratvert has a great channel, so that's going to be my text.
And here maybe I'll just make the error again where I don't have the T.
Now right beneath that, here I could use print and maybe I say let's print the text
and I want to print this three times.
So, I'll insert it in three times right here.
I'm going to delete this earlier example here so we just have the function.
So, I have my function now, can I run it?
Let's try clicking on run. So I click on run, and I get nothing back.
And the reason why is right up here, we've defined a function,
but we haven't actually called this function.
So, I've defined what should happen when I call this, but we haven't called it yet,
so here I'll go down and I'll backspace, so I'm out of this block of code that's
associated with this function, and here now I can call my function.
So just like we called the print function, here I could say print
and let's type in underscore Kevin and then I'll open and close my parentheses.
So right now, this will call the function. So, when Python sees print Kevin,
it'll look up to this definition for Kevin and then it'll execute this code.
So, let's click on run to see what happens.
Now look at that. Kevin Stravert has a great channel and it printed it out three times.
Oh, and look, there's that error in here.
So right up here, I could go to my function.
I could add the T and then I can hit run and it looks
like that's now successfully updated in all cases.
Now I could go through, and I could call this function multiple times.
This will really boost my ego.
So now when I hit run, look how many times it's printed out, Kevin has a great channel,
every single time I reference this function, it'll go back up here,
it'll look at the function definition, and then it'll run this code within that function.
Wth a function, to be able to call the function, I first need to define it before I can call it.
Here I'll remove these two references to the function
and so let's take the call of the function and I'll move it to the very top.
So here I call the function and then I define it.
So, if I hit run now here you get an error because here it says we'll print Kevin.
Well, it doesn't know about that function yet because it comes up later on in the code.
So once again, I need to make sure I call this function after I've defined my function.
So typically in code, you'll see all the different definitions or all of the
different definitions of the functions at the top.
One of the neat things too about using Visual Studio Code is here
when I click over in the function and I hover over, I can collapse this function.
So let's say I'm writing code and I want to have a whole bunch of functions that do different things.
I can collapse it and then that way it clears up my view a little bit and here
I could expand it if I need to jump into this function and update any of the code within.
With this one function that I defined on top, currently I don't pass anything into
the function and I also don't get anything back from the function.
If you remember the print example, here with print,
I'm passing in certain text that I want to print.
So basically, I'm sending in an argument or a parameter,
and I can do the same when I create a function.
So, let's say instead of entering the text here within the function, let me actually get rid of
this line right here, and right up here as part of my function definition, I'll type in text.
So, as I define my function, it's expecting me to pass in some value.
So, let's now go down here and look at the position where I'm calling my function.
It says print Kevin and here I can now pass in a value or basically pass in a parameter.
So, I'll type in Kevin Stratvert has a great channel.
So here you'll see as I call this function, it's passing in this parameter or this argument.
When I pass this in, here in the definition, it says it's expecting some text to be passed in
and down below the print is taking that text that I pass into this function.
So now when I hit run, here you'll see the same result.
Kevin Stratvert has a great channel
and this is just an example of how you can pass values into your function.
Next, I want to show you how we can put an if statement within a function.
So here again I'll type in def.
This will define my function and I'm going to call this school age calculator.
So, I want to basically determine based on a child's age,
where should they be in school, and I want to get two different values.
I want to get the child's age, so I'll type in age as one of the
parameters or arguments I want to get, and I also want the name of the child.
Now, just like we did before, let's put in a colon here and then let's press enter.
Here once again, you'll see that it automatically indents me and
so that shows that whatever code I write here is part of this function.
Now I want to insert my if statement, so I'm going to check first off if the age is less than five.
Once again, I'll insert the colon, and when I press enter, here it indents me even more so.
Now I'm within this if statement,
so if this evaluates to true, we're going to execute this code.
If it's true, I want to display some text, so here I'll call the print function.
Here I'll open it up and maybe I show some text that says
enjoy the time. You're still a young guy, you don't need to be in school yet.
So I've typed in some text. Now earlier we've just been printing out text,
but I can also print out variables together with text.
So here I could enter a comma and then I'll type in the name.
Here I'll type in another comma and let me enter in quotes again, and I'll say
is only, here I'll enter another comma, and then I'll type in the variable age.
So here you can see what it'll do, let's say the age is 3 and the name is Thomas.
It'll say enjoy the time, Thomas is only three, so that's what will display if he's under 5.
Let me hit enter and here now I want to enter another condition,
so I'll hit back space so I go back, and here I'll enter elif, basically else if
and I want to say if age let's say, is equivalent to five,
then I'll enter the colon and here maybe I'll say enjoy kindergarten, and then I'll show the name.
So here I'll type in print and then I'll open the parentheses
and I'll type in the quotes and here we'll say enjoy kindergarten,
and here I'll type in a comma and let me type in another comma here and then I'll display the name.
So here it'll say enjoy kindergarten, Thomas.
And lastly, I want to add one more condition, so I'll hit enter, backspace, and here I can
say else, colon, and here, maybe I'll say print and this one, I'll just display text and I'll
say they grow up so fast exclamation mark. I've now finished defining my function and I
have all of the different conditions within the function, so here I could enter down,
and I'll press backspace twice, so I exit out of both the conditions and also the function.
So now here I can call my function. So,
I'll call school age calculator and here I need to pass in two different values.
I'll pass in the age, I'll enter a comma, and then I'll type in the name, Thomas.
So now if I run this, here you'll see that it calls the function and then it goes through
all of these different conditions, and so here, while Thomas is less than five, he's only three,
so it says enjoy the time, Thomas is only three, and here we can test it out,
here I'll change it to five, and if I run it here, it says enjoy kindergarten, Thomas,
and let's say Thomas is now 10, and I'll run it, and here it says they grow up so fast.
So here now you see how we can call a function and here we pass in values into that function,
and it uses those values to run an if statement and to evaluate which one is true.
Next I want to show you how you can also get a parameter back from your function.
So so far, we've looked at how you could just run a function on its own, how you could pass values
into the function, and now we're going to look at how you can get a value back from the function.
I'm going to go through, let's remove this code right here, and let's start again from scratch.
For this one, it's just going to be a really simple example.
I want to know what is your age going to be in 10 years and we'll use a function to do this.
So here once again, let's define a function by typing in def
and here the function name will be add ten to age.
Once I've typed in the function name,
here I want to get one bit of input into my function or one parameter.
Here I'll type in the age, so someone will send in their age,
and then the function will add 10 to that age.
At the end of the definition of the function, let's enter a colon and hit enter.
Here this automatically indents me and now right now I want to figure out what the new age is.
So here I'll create a variable called New Age
and I want to set that equal to the age that's being passed in.
So, I'll type in age and I'm going to add 10 to it, and right underneath that now
once the function runs through and it does its magic, I want to return that value,
so here I'll type in return, and I want to return the new age, so I'll select this.
This will send the value back or return the value once the function is done running.
Here now, I want to call my function, and when I call the function,
I can assign that return value to a variable.
So here maybe I create a new variable called How old will
I be and I can set that equal to my function.
So here I'll call the function add ten to age
and here I want to pass in let's say my son who’s three, so I'll pass in three.
So once again, if I run this right now, it won't actually do anything.
It's assigning the output, which is 13 to how old will I be, but now I need to print it out.
So right down here let me type in print and I'm going to print in how old will I be.
And now if I hit run, here we'll see that that comes back as 13.
Now once again, just to see how this works, here I'm saying how old will I be?
This is a variable and I'm assigning this value to it, which is basically my function of add
ten to age, and I'm passing in three, so here it gets the age of three, it takes 3, adds 10,
it assigns its new age and once it's done running through the function, it returns the new age.
So, the new age is 13 and it assigns 13 to how old will I be and then here it prints out 13.
So that's how it works, and that's how you can get or you could return a value from a function.
Next, we're going to look at how you can use loops.
What is a loop?
Basically, it allows you to execute a block of code multiple times, so think of it this way.
Every single week my wife comes to me and says, Kevin,
can you take out the trash, and she asks me that every single week.
So, in a sense, that's kind of like a loop.
All right, let's jump on the PC and let's see how we can create a loop in Python.
So, let's now create a loop and there are two different types of loops.
One of them is called a while loop and the other one is called a for loop.
We're going to start with a while loop, and it's actually pretty easy to do.
I'm going to create a variable, just call it X and I'll assign it the value of 0.
And so here now I can type in a while loop.
So, I'll say, let's say while and let's say X is less than five.
So, while this value is less than five, I want it to execute some code, so here I'll insert a colon.
We do this with our if statements, with our functions.
Here when I hit enter now, it automatically indents me, so I'm now within the loop.
And here I could just say let's say print X, so I'll enter that in and then right after I print X,
I want to make sure I increment X, otherwise it will be an infinite loop.
So here I'll type in X = X + 1, just a really simple example.
We start out at zero and here it will say if X is less than five,
in which case it starts at zero. It is, so then it prints X, and then we add one. So
now X is 1 and X is still less than five, so it'll keep executing until it reaches 4.
So, let's run this to see how it works. So here it prints out 01234 and then once X = 5,
well, it's no longer less than five, so then we exit our loop and it's all done.
Note, that's the basics of how you can create just a very simple loop.
There's also another loop called a for loop, so I'll go down right here and let's type in for.
And this is also pretty simple. Here I can type in for and let's say 4 X in range, let's say five
through 10, and then here I'll close the parentheses,
enter a colon, and here too, I'll print the value of X.
Let me delete the code up above, and here what it'll do is it'll go through that range,
so when I hit run here, you see that it starts at 5 and it goes all the way up until 10,
but it doesn't include 10, so this is another form of a loop that you can use.
You can do some pretty neat things with loops. Here for example, I have the variable days and
I have an array assigned to it and these are just all the days of the week.
Here I can use a for loop to write out all the days of the week, so here I could say for d,
here I'm creating a variable, and I'll say in days, so here I'm looking at this variable.
Here I'll insert a colon and maybe I just want to print out the value of d. So, as it goes through
each day of the week, and here I can enter run and here it'll go through the variable of days,
and here it prints out every single day of the week, so that's pretty cool.
Now, one of the neat things too is you can start using some of the logic that we learned up above
in your loops, so let's say that I want to know what are all of the days before
Thursday, and once we hit Thursday, I want you to stop.
Here I can insert an if statement, so I'll say if and let's say if d is equivalent to let's say
Thursday, so I'll type in Thursday, and at this point I want it to stop. So I'll type in break.
So here if we click on run, here you'll see it goes through Monday, Tuesday,
Wednesday and then it looks like it hits Thursday, and at that point we stop the loop.
So, at that point we break,
and we no longer print any of the other days. With loops, we can also skip over items.
So, let's say that once we get to Thursday, I don't want it to include Thursday in the list,
but I still want it to continue and look at Friday, Saturday,
and Sunday. Instead of using break, I can use something called continue.
So now when I run the code, here you'll see Monday, Tuesday, Wednesday,
and then it found Thursday, and we simply want to skip over that item.
So, we added continue.
So here you see it skips over and then we get Friday, Saturday and Sunday.
So once again you can use logic in your loops.
You could also have it break and continue. So far throughout this video,
we've been looking at some of the fundamentals, and we've been writing all of our own code;
however, one thing you can do is you can build on top of what others have already done
using libraries and also modules, and there are lots of fantastic libraries that you can use.
Let's say for instance that we want to print out the value of Pi.
It turns out there's an existing library called math.
We could simply type in import and type in math,
and right beneath that, let's use our standard print function, and here I'll type in print.
And why don't we say something like pi is,
and then I'll insert a comma and here now I can refer to the math library and I'll type in .pi.
So, I want to get the pi value back
and here as I'm typing that out, you'll see all sorts of suggestions of what I could use.
So here when I click on run now, here it'll print out the value of pi.
So once again, when you're programming, you don't necessarily have to write everything on your own.
Instead, you can build on top of what others have done. If you were following along today,
you might have occasionally run into different errors as you were trying to execute your code
and they can really be a pain to resolve.
I want to go through three of the key errors that you might run into and how you can resolve them.
So, let's take one example.
Here I'm going to type in print, and I'll type in Hello World.
Now if you've been following along, you probably know that every time I type in this function,
and I type in text, I need to include my quotes around this, but I haven't done that.
When I hit run right now, here I get an error,
and this is referred to as a syntax error and the reason why is, I didn't follow
the rules of the print function, or I didn't follow the syntax rules for Python.
The best way to troubleshoot these is to simply look through your code
to find out where the error might be.
So here I get name error hello world is not defined.
So here it thinks hello world is a variable.
So, this is one way where you can look at the error message down here and that'll help you
troubleshoot up above what the problem is. Now you might run into another type of error, let's say I
take 10 / 0 and then I try to run this, and we all know that you can't divide by zero. Right here I
get a zero-division error division by zero. This is referred to as a runtime error. It just fails.
Now you could look down here at the error message to see what it was and that might
help you troubleshoot where the problem is in your code, and typically when you get an error message,
you could go to something like stackoverflow.com and you can look up your error message to see
if other people have encountered similar errors and that'll help you get down to the root cause.
And lastly, there's another type of error that you might encounter.
Let's say I type in name equals. Let's say Kevin,
just like we did earlier and here now, let's say I want to print, and I'll say hello name.
So, let's say I want to print the name that I assigned to this variable.
Here let me insert the parentheses and then I'll hit run.
So down here, it just says hello name, and it's not printing out Kevin. Now these errors here
these are referred to as semantic errors and these are notoriously hard to troubleshoot and
the reason why is because everything is working as it should based on how you programmed it.
But you're not getting the expected result.
So, for these you typically have to sit down, look through your code, evaluate
is everything working how it should, so these will tend to take more time.
All right, well that now brings us to the end of this video.
Hopefully by now you understand the fundamentals of programming using Python.
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All right, well that's all I had for you today,
I hope you enjoyed and as always, I hope to see you next time, bye.