CODESARRAY

Lesson 1, 2 October 2026, 4 min read

Your first Python program

Install Python 3.14, run it two ways, and read an eleven-line program one line at a time.

By the end of this page you will have Python installed, you will have run a program two different ways, and you will know the one rule that makes Python look different from every other language.

Install it

Go to python.org and download Python 3.14. On Windows, tick the box that says Add Python to PATH before you click install. Without it, the terminal will not know what python means.

Then open a terminal and check:

python --version
Python 3.14.7

If you see a version that starts with 3.14, you are ready.

Two ways to run Python

The first is the REPL, the interactive shell. Type python on its own and press enter. You get a prompt with three angle brackets, and Python answers each line as soon as you type it:

>>> 2 + 3
5

The REPL is for experimenting. Since 3.14 it even colours your code as you type.

The second way is a file. Save your code as hello.py and run it with:

python hello.py

Files are for programs you want to keep and run again. Everything in this series lives in files.

The program

# my first Python program
print("Hello, World!")

name = "Ada"
print("Hello,", name)

age = 36
if age >= 18:
    print(name, "is an adult")
    print("Welcome aboard")
print("Done")

Line by line:

  • Line 1 is a comment. Anything after a # is ignored by Python; it is a note for humans.
  • Line 2 calls print, the function that shows text on screen.
  • Line 4 stores the text "Ada" in a variable called name.
  • Line 5 prints two things at once. print puts a space between them.
  • Line 7 stores a number.
  • Line 8 asks a question: is age at least 18?
  • Lines 9 and 10 run only if the answer is yes.
  • Line 11 always runs.

The rule: indentation is the code

Python has no curly braces. The lines that belong to the if are the ones indented underneath it. Four spaces is the convention. The moment you go back to the left margin, you are outside the block.

If you forget to indent, Python refuses to run the file:

IndentationError: expected an indented block after 'if' statement on line 2

In Python, the whitespace is the code.

Run it

Python reads the file from top to bottom:

Hello, World!
Hello, Ada
Ada is an adult
Welcome aboard
Done

Because 36 is at least 18, both lines inside the if run, and then Done.

What you learned

  • python --version checks your install.
  • python on its own opens the REPL.
  • python hello.py runs a file.
  • print(...) shows output.
  • # starts a comment.
  • Four spaces of indentation make a block.

Next in the series: variables and types.

This article goes with the video Hello, Python. Watch it on YouTube.