Getting Started with Python

Why Learn Python?

Installing Python

Python comes pre-installed on macOS and most Linux distributions. Let's verify or set it up.

Check Your Current Version

Open a terminal and run:

python3 --version

Python 3.12.2

If you see version 3.8 or higher, you're ready. Otherwise, follow the steps below.

Install on macOS

# Using Homebrew (recommended)
brew install python3

# Verify
python3 --version
pip3 --version

Install on Ubuntu/Debian

sudo apt update
sudo apt install python3 python3-pip python3-venv

python3 --version

Install on Windows

The Python REPL

The REPL stands for Read-Eval-Print Loop. It's Python's interactive interpreter — think of it as a scratchpad where you can type Python code and see results instantly. No need to create a file, no need to run a command. Just type and get answers.

This is one of Python's greatest learning tools. Professional developers use it daily to test ideas, debug code, and explore libraries. You should have it open whenever you're coding.

Starting the REPL

Open your terminal (Terminal on Mac, Command Prompt on Windows, or any shell on Linux) and type python3:

$ python3
Python 3.12.2 (main, Feb  6 2024, 20:19:44)
Type "help", "copyright", "credits" for more information.
>>>

Try Some Expressions

The >>> prompt means Python is waiting for your input. Type any expression and press Enter — Python evaluates it immediately and shows the result. This instant feedback makes it perfect for learning:

>>> 2 + 3
5
>>> "Hello" + " " + "World"
'Hello World'
>>> len("Python")
6
>>> type(42)

>>> 2 ** 10
1024

Use It as a Calculator

Python makes an excellent calculator. Notice the difference between / (true division, always returns a decimal) and // (floor division, rounds down to a whole number). The ** operator is for exponentiation — much cleaner than calling a power function:

>>> 10 / 3      # True division (float result)
3.3333333333333335
>>> 10 // 3     # Floor division (integer result)
3
>>> 10 % 3      # Modulo (remainder)
1
>>> 2 ** 8      # Exponentiation
256
>>> abs(-42)    # Absolute value
42

Type exit() or press Ctrl+D to leave the REPL.

Your First Python Program

The REPL is great for experiments, but real programs live in files. A Python file is just a plain text file with a .py extension. You write your code in it, save it, and run it from the terminal. Unlike compiled languages like Java or C++, there's no compilation step — Python reads and executes your file directly.

Let's create your first program. This is a rite of passage for every programmer — the classic "Hello, World!" — but we'll make it more interesting by also using variables and f-strings.

Create hello.py

Open your text editor (VS Code, PyCharm, or even Notepad) and create a new file called hello.py. Type the following code exactly as shown — pay attention to the indentation and quotation marks:

# hello.py

print("Hello, World!")
print("Welcome to Python!")

# Variables need no type declaration
name = "Pythonista"
age = 1  # days of experience

# f-strings for formatted output (Python 3.6+)
print(f"Hello, {name}!")
print(f"You have {age} day(s) of Python experience.")
print(f"By tomorrow, that will be {age + 1}!")

Run It

Save the file and go back to your terminal. Navigate to the folder where you saved hello.py and run it:

python3 hello.py

Hello, World!
Welcome to Python!
Hello, Pythonista!
You have 1 day(s) of Python experience.
By tomorrow, that will be 2!

Understanding the Code

Let's break down every line. Understanding what each piece does is more important than memorizing syntax — once you understand the concepts, the syntax becomes natural:

Setting Up Your IDE

A good IDE makes Python development much more productive with autocomplete, debugging, and error highlighting.

VS Code (Recommended)

Editor Comparison

The Python Philosophy

Python has guiding principles called "The Zen of Python":

>>> import this

Beautiful is better than ugly.
Explicit is better than implicit.
Simple is better than complex.
Complex is better than complicated.
Flat is better than nested.
Readability counts.
...

PEP 8 — The Style Guide

PEP 8 is Python's official style guide. Following it makes your code readable:

# snake_case for variables and functions
my_variable = 42
def calculate_total(items):
    return sum(items)

# PascalCase for classes
class ShoppingCart:
    pass

# UPPER_CASE for constants
MAX_RETRIES = 3
DEFAULT_TIMEOUT = 30

print "Hello, World!"    # SyntaxError in Python 3!
raw_input("Name: ")      # NameError in Python 3

print("Hello, World!")   # Python 3
input("Name: ")          # Python 3

Next Steps

You've installed Python, explored the REPL, written your first program, and set up your IDE. Next: Variables & Data Types.