Python

TL;DR

One-liner: Python is a readable, versatile language that lets you write less code to do more.

Core Strengths:

• Readable syntax that reads like English
• Huge ecosystem for data science, web, automation, AI
• Batteries included - rich standard library
• Cross-platform and beginner-friendly

Philosophy

Python follows “The Zen of Python” - run import this to see it. Key principles:

• Readability counts - Code is read more than written
• Explicit is better than implicit - No hidden magic
• Simple is better than complex - Solve problems the straightforward way
• There should be one obvious way to do it - Unlike Perl’s TIMTOWTDI

Python is dynamically typed (no need to declare variable types) and uses indentation instead of braces. This forces clean, readable code.

Quick Start

Install

# macOS
brew install python

# Ubuntu/Debian
sudo apt install python3 python3-pip

# Windows: Download from python.org, check "Add to PATH"

Verify (latest stable: 3.13.1)

python3 --version  # Python 3.13.1
pip3 --version

First Program

# hello.py
print("Hello, Python!")

python3 hello.py

Interactive Mode

python3
>>> 2 + 2
4
>>> exit()

Language Essentials

Variables & Types

# No type declarations needed
name = "Alice"          # str
age = 25                # int
height = 1.75           # float
is_student = True       # bool
items = [1, 2, 3]       # list
data = {"key": "value"} # dict

# Check type
type(name)  # <class 'str'>

Control Flow

# if/elif/else
if age >= 18:
    print("Adult")
elif age >= 13:
    print("Teen")
else:
    print("Child")

# for loop
for item in items:
    print(item)

for i in range(5):  # 0, 1, 2, 3, 4
    print(i)

# while loop
while count > 0:
    count -= 1

Functions

def greet(name, greeting="Hello"):
    """Docstring: describes the function"""
    return f"{greeting}, {name}!"

# Call
greet("World")           # "Hello, World!"
greet("World", "Hi")     # "Hi, World!"

# Lambda (anonymous function)
square = lambda x: x ** 2

Error Handling

try:
    result = 10 / 0
except ZeroDivisionError:
    print("Cannot divide by zero")
except Exception as e:
    print(f"Error: {e}")
finally:
    print("Always runs")

List Comprehension

# Powerful one-liner for transforming lists
squares = [x**2 for x in range(10)]
evens = [x for x in range(10) if x % 2 == 0]

Gotchas

python vs python3

# On many systems, 'python' may point to Python 2 or not exist
# Always use python3 explicitly
python3 --version

Indentation is syntax

# Python uses indentation (4 spaces) instead of braces
if True:
    print("Correct")  # 4 spaces
   print("Wrong")     # IndentationError!

Mutable default arguments

# WRONG: list is shared across calls
def add_item(item, items=[]):
    items.append(item)
    return items

# RIGHT: use None
def add_item(item, items=None):
    if items is None:
        items = []
    items.append(item)
    return items

Virtual environments

# Always use venv for projects to avoid dependency conflicts
python3 -m venv venv
source venv/bin/activate  # Linux/macOS
pip install package
deactivate

When to Choose

Best for:

• Data science & machine learning (pandas, scikit-learn, PyTorch)
• Quick scripts and automation
• Web backends (Django, FastAPI, Flask)
• Beginners learning programming

Not ideal for:

• Mobile apps (use Swift, Kotlin)
• High-performance computing (use C++, Rust)
• Frontend web (use JavaScript)

Comparison:

Aspect	Python	JavaScript	Go
Typing	Dynamic	Dynamic	Static
Speed	Slower	Medium	Fast
Use case	Data/AI/Scripts	Web/Full-stack	Backend/CLI
Learning curve	Easy	Easy	Medium

Next Steps

• Official Tutorial - Start here
• Real Python - Practical tutorials
• PyPI - Package repository
• Automate the Boring Stuff - Free book

Ecosystem

Package Manager

pip install package        # Install
pip freeze > requirements.txt  # Export deps
pip install -r requirements.txt  # Install from file

Popular Frameworks

• Web: Django, FastAPI, Flask
• Data: pandas, NumPy, matplotlib
• ML/AI: PyTorch, TensorFlow, scikit-learn
• Automation: requests, BeautifulSoup, Selenium