What is a program?

Everything you do on the computer has a computer program — “software” — behind the scenes.

We write computer programs to help us solve problems or perform tasks, like editing documents, browsing web pages, sharing images, or chatting with friends.

Everything on a computer is a program behind the scenes.

This very moment, you are reading on a computer, with a web browser. The browser is a program, built by a large team. But, how do they actually do it? What does a program look like when they are writing it? How does it work?

This is the question we'll focus on first: What are computer programs?

  • Programming languages let us write instructions for computers using words
  • Programming languages get translated into 1s and 0s the machine understands
  • Python is a beginner-friendly language that has tons of real-world use
  • You can make basic programs in Python using print, input, +, and =

Programs are...

Programs are text that a computer can execute as instructions.

That means you can read them and write them with the keyboard.

Programs use special symbols and keywords. The symbols and the order they have to go in is called the syntax.

If a program has valid syntax, then the computer can run it. If the program has the right logic, it will do what the programmer wanted. The syntax, grammar, and vocabulary make up a Programming Language.

We're learning Python, so we're going to learn what words and symbols are allowed in Python, and how to structure them to make the computer do what we want.

Translating for machines

Underneath the screens and keyboards, computers are mechanical. They only understand 1s and 0s. But, people don’t think in 1s and 0s! When you want something, you use words.

So, how do we tell computers what we want them to do, like “send a message” or “show this webpage”?

We need a translator.

Programming languages let us write instructions for computers using words. Those words translate into instructions that the machine understands (1s and 0s). Then, we can type something like “send a message”, and it’ll get translated into something like 00011101001010001 001010010001001 101000010010100 10001010001010100000 01001010010, which will make the computer send the message.

A Very Picky Translator

Programming languages are very picky about what you type in. You can’t actually type in send a message — the programming language wouldn’t understand! Instead, it would be more like send_message("Hello!") . The program has to be crafted precisely, with lots of attention to detail, so that the programming language knows exactly what you mean.

Programming languages only understand a few specific words and symbols, in a few specific combinations. Those words, symbols, and combinations are the vocabulary, grammar and syntax of a programming language — and that’s what you’ll learn in this course!

What is Python?

Python is a programming language. You can write Python code, and then it will turn into instructions the computer understands and runs.

Here’s a small program that prints out 10 copies of the word “Programming”.

message = "Programming"
number_of_copies = 10

print(message * number_of_copies) # ProgrammingProgrammingProgrammingProgrammingProgrammingProgrammingProgrammingProgrammingProgrammingProgramming

As you can see:

  • It uses words, like message and print and numbers like 10
  • It uses symbols like = , *, and ()
  • The words and symbols are arranged in a particular order

What is python used for?

  • Python is a general purpose programming language, which means it’s a good fit for a wide variety of problems.
  • Python is popular for data science, mathematics, web development, and more. It’s commonly used for “scripting” - small programs to do specific tasks.
  • Python is a widely recommended language for beginners. The syntax is not as hard to get started with as some other languages, and you can build cool, real-world projects with it.

How do you write programs?

We need two things to start writing programs of our own:

  1. A Text Editor: A tool to write text
  2. An Interpreter or a Compiler: A tool to translate your code to computer-executable programs.

In this course, we recommend using VSCode as your text editor, and the built-in terminal for VSCode to run the Python interpreter.

We'll also use Replit for other helpful features: multiplayer mode and sharing.

Further Exploration: Plain text vs. Rich text

Why not use something like Google Docs to write code?

Google docs is awesome for writing formatted text. It's got highlighting, different fonts, sizes, alignment, tables, and lots of different options for formatting.

But... Python doesn't understand any of that formatting. Python only understands the text. That's true of most programming languages: they only consist of text.

Google docs is known as a "Rich Text Editor". It's the text, plus the formatting.

For programming, we use something called a "Plain Text Editor", or just "Text Editor". That means we can't use bold, center, or other formatting options. We only type the characters and symbols.

But... in the examples above, the code has colors!?

Text Editors for programming have features like Syntax Highlighting that display your code in color to help you. The colors aren't saved with the code, and you can't change them word-by-word. Replit has built-in features like Syntax Highlighting, so you don't have to worry about it as long as you're using Replit.

A Brief Tour of Python

Over the next few weeks, you’ll learn about Python in more detail.

First, we'll quickly illustrate some of the basics, to get you started.

Comments: Explaining your code

Programs are written and read by people.

That means that when writing code, we prioritize both making the computer do what we want and making sure someone else can understand what the code means.

We can help others make sense of our code through its structure, and with comments.

📺 Watch this video to learn about comments.

In the example below, the first two lines are code comments.

# Prints "Programming" ten times
# string * number copies the string that many times
message = "Programming"
number_of_copies = 10
print(message * number_of_copies)

Comments communicate with the other people that read our code. While code can sometimes make sense on its own, comments fill gaps in explanation.

In Python, comments start with the # character (called ‘hash’ or ‘octothorp’). Anything after the # gets ignored by Python - it won’t try to run it as code.

In Kibo, we’ll often use comments to explain code and to illustrate what code does. When you see a snippet like:

# prints message lots of times
print(message * number_of_copies)
# => ProgrammingProgrammingProgrammingProgrammingProgrammingProgrammingProgrammingProgrammingProgramming

The comments explain the result of running the code.

The easiest way to make your program display some result is to use print.

Here’s an example:

print("This is the output")

The program would output:

This is the output
  • You use the keyword print
  • Then parentheses
  • Inside the ( ) you put the value you want to show
  • Text has to go in inside quote marks " "

To run code in line with the lessons, we'll use Trinket,

Click the ▶️ button to run the program and see the output.

Variables: Storing values to reuse

You can give a value a name, and use it later, using a variable.

message = "I love programming"
print(message)
print(message)
print(message)

message is a variable. It stores the value "I love programming".

The equals sign = assigns the value to the variable.

The program would output:

I love programming
I love programming
I love programming

Click the ▶️ button to run the program and see the output.

Adding things together with +

In Python, you can add things together with the + operator.

print(10 + 10) # 20
print(10 + 154) # 164
print(12345 + 23456) # 35801

Computers are good at arithmetic — they are very fancy calculators.

Python can also add text together with +:

message = " loves programming"
print("Adesola" + message)
print("Chidi" + message)
print("Ebbe" + message)

The program would output:

Adesola loves programming
Chidi loves programming
Ebbe loves programming

Click the ▶️ button to run the program and see the output.

Input: get some data from the user

Python can ask the user to type in a message using input.

favorite = input("What is your favorite thing? ")
print("I like " + favorite + " too!")

When the program sees input, it prints the message and waits for the user to enter their response. Then, it continues from there.

The variable favorite stores the value that the user typed in.

If the user typed in playing soccer, then the output would look like:

What is your favorite thing? playing soccer I like playing soccer too!

When you run this program, be sure to click in the “Result” box to type a response, and press Enter.

In summary

  • Programming languages get translated into 1s and 0s the machine understands
  • Python is a beginner-friendly language that has tons of real-world use
  • You can make basic programs in Python using print, input, +, and =