CODESARRAY

Lesson 1, by Codesarray, , 4 min read

Python Hello World: your first program, step by step

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

This is the Python Hello World lesson, the first in the beginner track. By the end of this page you will have Python 3.14 installed, you will have run a Python 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.

Common questions

Which editor should I write Python in? Any text editor that saves plain text works: the file just has to end in .py. Visual Studio Code is free and the most common choice; Python also installs a small editor of its own called IDLE. Do not use a word processor, which adds formatting Python cannot read.

**The terminal says python is not recognised. What now?** On Windows that almost always means the "Add Python to PATH" box was not ticked. Run the installer again, choose Modify, and tick it. On macOS and Linux the command is often python3 instead of python; try that first.

**Does print("Hello, World!") need the brackets?** Yes. In Python 3, print is a function, and a function is called with brackets around what you give it. Writing print "Hello" without them is a syntax error.

Do I have to use exactly four spaces? Python accepts any consistent indentation inside one block, but four spaces is the convention the whole Python world follows, and mixing tabs and spaces in one file is an error. Set your editor to insert four spaces when you press Tab and you will never think about it again.

What happens if I run the file twice? The same thing twice. A file is a recipe: every run starts from the top with nothing remembered from before. That is the difference from the REPL, which keeps values until you close it.

Next in the series: Variables and types.

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