1. What is Python?

Python: A high-level, interpreted, general-purpose programming language known for its clear, readable syntax. Created by Guido van Rossum; first released in 1991.

Key Characteristics

Feature	What It Means
High-level	Handles complex details (memory, hardware) automatically so you focus on problem-solving
Interpreted	Code runs line by line (not compiled all at once); easy to test and debug
Dynamically typed	No need to declare variable types; Python figures them out (`x = 5` not `int x = 5`)
Indentation-based	Uses whitespace to define code blocks instead of curly braces `{}`
General-purpose	Suitable for web, data science, AI, automation, games, science, and more

Brief History

1989: Guido van Rossum begins working on Python
1991: First public release (version 0.9.0)
2000: Python 2.0 released
2008: Python 3.0 released (major redesign)
2020: Python 2 officially retired
Today: Python 3 is the standard; consistently #1-2 most popular language

The name "Python" comes from Monty Python's Flying Circus, not the snake!

Real-World Applications

Area	Examples
Web Development	Django, Flask (Instagram, Pinterest)
Data Science	pandas, NumPy, matplotlib
AI/ML	TensorFlow, PyTorch, scikit-learn
Automation	File management, web scraping, email
Scientific Computing	NASA, CERN, university research
Game Development	Pygame for 2D games

2. Installing Python

Installation Steps

Windows

Go to python.org/downloads
Download the latest Python 3.x installer
Run the .exe installer
CHECK "Add python.exe to PATH" (critical!)
Click "Install Now"

Most common Windows mistake: forgetting to check "Add Python to PATH." If forgotten, uninstall and reinstall with the checkbox checked.

Mac

Go to python.org/downloads
Download the macOS installer (.pkg)
Run the installer and follow prompts
Use python3 command (not python) in Terminal

Linux

Python 3 often comes pre-installed
Check with: python3 --version
If needed: sudo apt install python3 python3-pip (Ubuntu/Debian)

Verifying Installation

python --version # or python3 --version on Mac/Linux

Should display something like: Python 3.12.1

PATH: An environment variable that tells your operating system where to look for programs. Python must be in your PATH for the python command to work in the terminal.

Text Editors & IDEs

Editor	Best For	Note
IDLE	Getting started immediately	Comes with Python
VS Code	Best overall choice	Free, install Python extension
Thonny	Absolute beginners	Built-in Python, great debugger
Sublime Text	Fast, lightweight editing	Free evaluation available

3. Your First Python Program

The print() Function

print(): A built-in Python function that displays text or values on the screen. The most basic way to see output from your program.

Usage Patterns

      # Basic text

      print("Hello, World!")

      # Numbers (no quotes needed)

      print(42)

      print(3.14)

      # Multiple items (spaces added automatically)

      print("The answer is", 42)

      # Math inside print

      print("Sum:", 3 + 4)   # Output: Sum: 7

      # Empty line

      print()

Strings (Text)

Text must be wrapped in quotes (single ' or double ")
Both work the same: "hello" and 'hello'
Use double quotes when text has apostrophes: "It's fun"
Use single quotes when text has double quotes: 'She said "hi"'

Comments

Comments: Notes in your code that Python ignores. Start with #. Used to explain code, leave notes, or disable lines temporarily.

      # This entire line is a comment

      print("Hello")  # This part is a comment

      # print("This won't run")

Python Files

Save with .py extension (e.g., hello.py)
Use lowercase and underscores: my_program.py
No spaces in filenames
Never name a file python.py
Run from command line: python hello.py
Run from IDLE: press F5

Common Errors

Error	Cause	Fix
SyntaxError: invalid syntax	Missing quotes around text	Add quotes: `print("Hello")`
SyntaxError: unterminated string	Mismatched quotes	Match open/close quotes
SyntaxError: Missing parentheses	Forgot parentheses	Use: `print("text")`
NameError: name 'Print' not defined	Wrong capitalization	Use lowercase: `print`

Python is CASE-SENSITIVE. print() works. Print(), PRINT() do NOT.

4. The Python Interpreter (REPL)

REPL: Read-Eval-Print-Loop. An interactive environment where you type Python code one line at a time and see results immediately.

Starting and Exiting

      # Start the interpreter

      python        # (or python3 on Mac/Linux)

      # Exit the interpreter

      exit()       # or quit()

      # Ctrl+D (Mac/Linux) or Ctrl+Z then Enter (Windows)

Arithmetic Operators

Operator	Name	Example	Result
`+`	Addition	`5 + 3`	8
`-`	Subtraction	`10 - 4`	6
`*`	Multiplication	`6 * 7`	42
`/`	Division (always float)	`15 / 4`	3.75
`//`	Integer division	`15 // 4`	3
`%`	Modulo (remainder)	`15 % 4`	3
`**`	Exponentiation	`2 ** 10`	1024

Order of Operations (PEMDAS)

Parentheses → Exponents → Multiplication/Division → Addition/Subtraction

2 + 3 * 4 = 14 (multiplication first)
(2 + 3) * 4 = 20 (parentheses first)

Data Types (Preview)

Type	Name	Examples
`int`	Integer	42, -7, 0, 1000
`float`	Floating-point	3.14, -0.5, 2.0
`str`	String	"hello", 'Python', "42"
`bool`	Boolean	True, False

Useful Built-in Functions

Function	Purpose	Example
`print()`	Display output	`print("Hello")`
`type()`	Check data type	`type(42)` → `<class 'int'>`
`help()`	Get documentation	`help(print)`

Interpreter vs. Script File

Use Interpreter For	Use Script File For
Quick calculations	Programs you want to save
Testing ideas	Multi-line programs
Exploring with type()/help()	Complete applications
Learning new functions	Homework assignments
Debugging values	Code to share with others

In the REPL, typing an expression shows its value automatically.
In a script file, you must use print() to see output.

Key Reminders

1. Python is case-sensitive: print() not Print()
2. Always check "Add to PATH" on Windows
3. Python files end in .py
4. Comments start with # and are ignored by Python
5. / gives float, // gives integer division
6. Quotes make text strings; no quotes for numbers
7. Use the REPL for testing, scripts for saving

Module 1: What is Python & Getting Started

Free Python Learning Platform • Safaa Dabagh • sdabagh.github.io

Module 1 Study Guide