Python for complete beginners · Unit 1: Getting started · Lesson 1 of 24

Lesson 1: What is programming? Your first Python program

Start here if you have never written code before. You'll find out what programming really is, meet Python, and write and run your very first program – right here in your browser.

⏱ About 30 minutesFor complete beginners: KS3 (Years 7–9) and adultsRuns in your browser – nothing to install

A program is a list of instructions

A program is a list of instructions that tells a computer what to do. That's it. Every app on a phone, every game, every website is made of instructions that a person wrote down.

You already know about instructions. A recipe is one: "Crack two eggs into a bowl. Whisk them. Pour them into a hot pan." You do the steps in order, from the top, one at a time. A computer program works the same way.

Programming (also called coding) is the job of writing those instructions. The instructions themselves are called code.

Computers are fast, but very literal

Here is the big difference between you and a computer. If a recipe says "add the eggs" and forgets to say "crack them first", you would still crack them. A computer would not. It does exactly what it is told – no more, no less – and it never guesses what you meant.

Try this with a friend: ask them to act as a robot and make a jam sandwich, following only your words. "Put the jam on the bread" might end with a whole jar balanced on a loaf! Programmers learn to give instructions that are clear, complete and in the right order. That is the real skill, and you will practise it in every lesson.

Programs are everywhere

• A phone alarm: when the time is 7:00, play a sound.
• Traffic lights: show green, wait, show amber, wait, show red.
• A game: if the player touches a coin, add 1 to the score.
• A washing machine: fill with water, spin, drain, spin faster.

Someone wrote each of those programs. By the end of this course, you will be able to write programs like them.

What is Python?

Deep down, a computer only understands long patterns of 0s and 1s. Nobody wants to write those! So people invented programming languages: ways of writing instructions that humans can read, which the computer can then turn into its own 0s and 1s.

Python is one of the most popular programming languages in the world. It was created by Guido van Rossum and first released in 1991. (It's named after the comedy show Monty Python's Flying Circus, not the snake.) People choose Python because:

• It reads almost like English. print("Hello") prints the word Hello.
• It's used for real work – in science, websites, games, data and artificial intelligence.
• It's great for beginners, so it's taught in many schools.

On this site, Python runs right inside your web browser. There is nothing to download or install, and your code stays on your own device.

How Python runs your code

When you press Run, a program called the interpreter reads your code. It starts at line 1, does what that line says, then moves to line 2, then line 3, and so on down to the end. Anything your program shows on the screen is called the output.

Doing the lines in order, from the top, is called sequence. It is the first of the big ideas in programming, and it's why the order of your lines matters.

Your first program

Since the 1970s, programmers learning a new language have started with the same tiny program: one that says Hello, World! It's also the motto of our Computing department. Press Run and watch the output box.

print("Hello, World!")

Congratulations – you are now a programmer! Let's look at what you wrote:

• print is an instruction built into Python. It means "show this on the screen". We call it a function; you'll learn more about functions later in the course.
• The round brackets ( ) hold the thing you want to print.
• The quote marks " " show where the text starts and ends. Text in quote marks is called a string.

The quote marks are not printed. They are just there to tell Python "this is text, not an instruction".

Meet the editor

The box you just used is the editor. Every lesson has several of them. Here is what each part does:

• The code area (with line numbers down the left). Click in it and type. Line numbers help when Python tells you about a problem on "line 2".
• Run runs your code. On a keyboard, Ctrl + Enter does the same.
• Output is where anything your program prints appears.
• Start again puts the original code back, so you can never break anything for good.

The first time you press Run, the page takes a moment to load Python. After that it's quick.

print("Hello, World!")

One line after another

A program can have as many lines as you like. Python runs them in order, from the top.

1print("Ready")
2print("Steady")
3print("Go!")

Ready
Steady
Go!

Each print starts a new line of output. Now swap the order: move print("Go!") to the top and run it. The output changes, because the order of the lines is the order of the instructions.

print("Ready")
print("Steady")
print("Go!")

Your turn

These exercises are checked by Classfern as soon as you press Check. If you get stuck, press Stuck? for a nudge, then a hint, and only then the answer. Getting things wrong is part of learning – nobody sees your attempts but you.

print("Hello, Classfern!")

Hip
Hip
Hooray!

print("3")
print("2")
print("1")
print("Blast off!")

print("My first program")
print("works!")

Common mistakes

Quick quiz

Five quick questions to check you've got the main ideas. They're marked as you go.

Recap

• A program is a list of instructions. Programming is writing them.
• Computers do exactly what they're told, in order, from the top (sequence).
• Python is a popular language that reads almost like English.
• print("…") shows text on the screen. Text in quote marks is a string.
• Capital letters, brackets and quote marks all matter.

Next lesson, you'll find out much more about print and strings: printing several things at once, numbers and sums, and quote marks inside text.

Python is a registered trademark of the Python Software Foundation. Classfern is independent and is not affiliated with or endorsed by it.

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