How to install Python and run your first script

Setting Up Python

Download Python from python.org. During installation on Windows, check Add Python to PATH. On macOS/Linux it is often pre-installed — confirm with python3 --version in your terminal.

Python runs in two modes. Interactive mode (python3) executes one line at a time. Script mode runs a .py file top-to-bottom. Use script mode for anything beyond quick experiments.

Your First Script

Create hello.py and run it with python3 hello.py.

# hello.py
print("Hello, World!")  # prints to stdout
print("Python version: 3.x")

Key Rules

Python uses indentation (4 spaces) instead of curly braces to define blocks — this is enforced by the interpreter, not style. A # starts a single-line comment. Python is case-sensitive: Print is not the same as print.

The print() function accepts multiple arguments separated by commas and adds a space between them by default. Pass sep= or end= to control output formatting.

print("a", "b", "c", sep="-")  # a-b-c
print("loading", end="...\n")   # loading...

When Python runs a script, the interpreter reads it line by line from top to bottom. Any syntax error stops execution immediately and prints the line number and a brief message — read error messages carefully rather than guessing the fix. The REPL (Read-Eval-Print Loop) in interactive mode is excellent for quick experiments, but scripts are reproducible and easier to share. Keep your working scripts in a project folder with a clear name like main.py or run.py. Use a virtual environment per project so dependencies stay isolated.