Introduction to Python

Create a new file called hello.py using any text editor:

nano hello.py

Type the following code:

# My first Python script
print("Hello, World!")
print("Welcome to Python programming!")

name = "Learner"
print("Hello, " + name + "!")

Save and run it:

python3 hello.py

Open a terminal and find out whether you already have Python

Go: open the terminal. Windows: press the Start button, type powershell, press Enter. macOS: press Cmd + Space, type terminal, press Enter. Linux: press Ctrl + Alt + T. A window opens with a blinking cursor; that is all a terminal is — a place to type commands instead of clicking.

Do: type python3 --version and press Enter. If that reports nothing useful, type python --version and press Enter.

You should see: a line such as Python 3.12.3. Any version beginning 3. works for everything on this site. Remember which of the two commands worked — that is the one you will use from now on. On many Linux and macOS machines only python3 exists; on Windows it is usually python.

If not: command not found from both means Python is genuinely not installed — go to step 2. If you see a version starting with 2., that is a retired version from a previous era; install a current one in step 2 and keep using the python3 name.

Install Python, only if step 1 found none

Go: if step 1 printed a version, skip this step entirely. Otherwise open python.org/downloads in your browser. Take it from there and nowhere else — Python is a frequent target for lookalike download sites.

Do: the site offers the right installer for your system automatically; download and run it. On Windows there is one setting that matters: on the installer's first screen, tick Add python.exe to PATH before pressing Install. On macOS and Linux there is nothing to choose.

You should see: after it finishes, close the terminal and open a new one, then repeat step 1. It should now print a version.

If not: still command not found on Windows almost always means that tickbox was missed — run the installer again, choose Modify, and enable it. Opening a fresh terminal matters too: a terminal that was already running does not notice a newly installed program.

Start Python and make it do something

Go: in the terminal, type python3 on its own (or python, whichever worked in step 1) and press Enter.

Do: at the >>> prompt, type 2 + 2 and press Enter. Then type print("Hello, world!") and press Enter.

You should see: first a banner naming your version, then >>>. After the first line, 4. After the second, Hello, world!. The >>> means Python is waiting for you — this is the interactive shell, and it answers immediately.

If not: if the prompt still shows your normal terminal instead of >>>, Python did not start; recheck step 1. If you typed print("Hello, world!) and nothing happens, you left off a quotation mark — Python is waiting for you to finish the line. Press Ctrl + C and type it again.

Leave the shell — the step nobody tells beginners

Go: stay where you are, at the >>> prompt.

Do: type exit(), with the two brackets, and press Enter.

You should see: the >>> disappears and your ordinary terminal prompt returns. You are out of Python and back in the terminal.

If not: typing exit without the brackets gets you Use exit() or Ctrl-D (i.e. EOF) to exit — Python telling you politely. This trips up almost everyone once. Knowing where you are matters: >>> means Python is listening and expects Python; anything else means the terminal is listening and expects commands like python3.

Write a program in a file and run it

Go: open a plain text editor. Windows: Notepad, from the Start menu. macOS: TextEdit, then choose Format → Make Plain Text. Linux: Text Editor / gedit. Any of these is fine for now; a programmer's editor comes later and changes nothing here.

Do: type these two lines, then save the file as hello.py in your home folder. In Notepad's Save dialog, set "Save as type" to "All Files" first, and in TextEdit untick "If no extension is provided, use .txt". Then in the terminal run cd ~ followed by python3 hello.py.

print("Hello, world!")
print("Python is working.")

You should see: two lines, Hello, world! and Python is working. You have just written and run a program.

If not: python3: can't open file '...hello.py': [Errno 2] No such file or directory has two causes and the message tells you which. If the path shown is not where you saved the file, the terminal is in the wrong folder — cd ~ moves to your home folder. If the path is right, your editor almost certainly saved hello.py.txt: that is the dialog setting above, and it is the single most common first-day obstacle. Turn on file extensions in your file manager so you can see the real name.

Cause an error on purpose, so errors stop being frightening

Go: open hello.py again in the same editor.

Do: delete the closing bracket from the first line so it reads print("Hello, world!", save, and run python3 hello.py again.

You should see: a SyntaxError naming the file and the line number. Read the line number first, every time — Python is telling you exactly where to look. Put the bracket back, save, run it again, and the two lines return.

If not: if it still prints normally, the file did not save; check the title bar of your editor for a dot or the word "edited". An error message is not a failure and never breaks anything — it is Python's only way of saying which character confused it. You will read thousands of them.