Overview

What is Python by Example?

Python by Example is a code-first tutorial series designed for experienced developers switching to Python or deepening their Python expertise. Instead of narrative explanations, you learn through 80 self-contained, heavily annotated, runnable examples that demonstrate Python concepts in action.

Why By-Example?

Traditional tutorials explain concepts with prose, then show code. By-example inverts this approach:

1. Show the code first - Working, production-relevant examples
2. Run it second - Every example is copy-paste-runnable
3. Understand through interaction - Inline annotations reveal behavior
4. Build pattern recognition - 80 examples create comprehensive mental models

This approach works best for developers who prefer learning through working code rather than reading documentation.

Learning Path

  %% Color Palette: Blue #0173B2, Orange #DE8F05, Teal #029E73, Purple #CC78BC, Brown #CA9161
graph TD
    A["Beginner<br/>Examples 1-27<br/>Python Fundamentals"] --> B["Intermediate<br/>Examples 28-54<br/>Production Patterns"]
    B --> C["Advanced<br/>Examples 55-80<br/>Expert Mastery"]

    style A fill:#0173B2,color:#fff
    style B fill:#DE8F05,color:#fff
    style C fill:#029E73,color:#fff

Progress from fundamentals through production patterns to expert mastery. Each level builds on the previous, increasing in sophistication and introducing more Pythonic idioms.

Coverage Philosophy

This tutorial provides 95% coverage of Python through practical, annotated examples. The 95% figure represents the depth and breadth of concepts covered, not a time estimate—focus is on outcomes and understanding, not duration.

What’s Covered

Included (95%):

• Core syntax and semantics (variables, operators, control flow)
• Built-in types and data structures (lists, dicts, sets, tuples)
• Functions, lambdas, and closures
• Object-oriented programming (classes, inheritance, magic methods)
• Modules and packages
• File I/O and context managers
• Exception handling and custom exceptions
• Decorators and descriptors
• Comprehensions and generators
• Itertools and functools
• Type hints and protocols
• Asyncio and concurrency
• Testing with pytest
• Standard library essentials (pathlib, collections, datetime, json)
• Virtual environments and packaging

What’s NOT Covered

This guide focuses on learning-oriented examples, not problem-solving recipes or production deployment. For additional topics:

• CPython internals and C extensions - Implementation details beyond the language
• Rare standard library modules - aifc, sunau, uu, and other niche modules
• Platform-specific features - ctypes internals, Windows registry
• Deprecated features - imp module, old-style classes
• Framework internals - Django ORM source, Flask internals (covered at introductory level only)

The 95% coverage goal maintains humility—no tutorial can cover everything. This guide teaches the core concepts that unlock the remaining 5% through your own exploration and project work.

Tutorial Structure

80 examples across three levels:

• Beginner (Examples 1-27, 0-40% coverage): Python fundamentals - variables, types, control flow, functions, basic data structures, simple OOP
• Intermediate (Examples 28-54, 40-75% coverage): Production patterns - modules, file I/O, exceptions, decorators, comprehensions, iterators, testing
• Advanced (Examples 55-80, 75-95% coverage): Expert mastery - metaclasses, asyncio, context managers, generators, protocols, type hints, packaging, performance

Coverage percentages indicate depth and breadth of Python knowledge, not time investment.

Example Format

Every example follows a five-part format:

1. Brief Explanation (2-3 sentences)

Context and motivation for the concept:

### Example 15: List Comprehensions

List comprehensions provide a concise syntax for creating lists based on existing sequences, combining mapping and filtering in a single expression. They are more readable and often faster than equivalent for-loop constructions, making them a Pythonic way to transform data.

2. Mermaid Diagram (when appropriate)

Visual representation for non-obvious concepts (30-50% of examples):

  %% List comprehension flow
graph TD
    A[Input List] --> B[For Each Element]
    B --> C{Filter Condition?}
    C -->|True| D[Transform Element]
    C -->|False| B
    D --> E[Add to Result]
    E --> B
    B --> F[Output List]

    style A fill:#0173B2,color:#fff
    style B fill:#DE8F05,color:#000
    style C fill:#CC78BC,color:#000
    style D fill:#029E73,color:#fff
    style E fill:#029E73,color:#fff
    style F fill:#0173B2,color:#fff

3. Heavily Annotated Code

Self-contained, runnable code with # => annotations showing outputs and states:

# Original list
numbers = [1, 2, 3, 4, 5]        # => numbers is [1, 2, 3, 4, 5]

# List comprehension: squares of even numbers
squares = [x**2 for x in numbers if x % 2 == 0]
                                  # => squares is [4, 16] (2^2=4, 4^2=16)

# Equivalent for-loop (for comparison)
squares_loop = []                # => squares_loop is []
for x in numbers:                # => Iterates: 1, 2, 3, 4, 5
    if x % 2 == 0:               # => True for 2, 4
        squares_loop.append(x**2)# => Appends 4, then 16
                                  # => squares_loop is [4, 16]

print(squares)                   # => Output: [4, 16]
print(squares == squares_loop)   # => Output: True

4. Key Takeaway (1-2 sentences)

Essential insight distilled:

**Key Takeaway**: Use list comprehensions for simple transformations and filtering - they're more Pythonic and readable than equivalent loops, but switch to regular loops when logic becomes complex or requires multiple statements.

How to Use This Tutorial

For Complete Beginners to Python

1. Start with Beginner level (Examples 1-27)
2. Run every example in a Python REPL or .py file
3. Modify examples to test your understanding
4. Progress to Intermediate when comfortable with basics

For Developers with Python Experience

1. Skim Beginner to identify gaps
2. Focus on Intermediate (Examples 28-54) for production patterns
3. Deep-dive Advanced (Examples 55-80) for expert techniques

For Experienced Developers from Other Languages

1. Review Beginner quickly to learn syntax differences
2. Focus on Pythonic idioms in Intermediate
3. Use Advanced as a reference for Python-specific features

Self-Containment Philosophy

Every example is copy-paste-runnable within its level scope:

• Beginner examples: Completely standalone - full imports, no dependencies on previous examples
• Intermediate examples: Assume beginner knowledge but include all necessary code to run
• Advanced examples: Assume beginner + intermediate concepts but remain fully runnable

Golden rule: If you delete all other examples, any single example should still run successfully.

Educational Annotations

Examples use # => notation to show:

• Variable states: x = 10 # => x is 10 (type: int)
• Outputs: print(x) # => Output: 10
• Intermediate values: y = x * 2 # => y is 20 (x remains 10)
• Side effects: lst.append(5) # => lst is now [1, 2, 3, 5]
• Error cases: int("bad") # => Raises ValueError: invalid literal for int()

These annotations make code behavior explicit without needing to run examples (though running them is encouraged!).

Diagram Guidelines

Diagrams use color-blind friendly palette:

• Blue (#0173B2): Primary elements, starting states
• Orange (#DE8F05): Processing states, operations
• Teal (#029E73): Success states, outputs
• Purple (#CC78BC): Conditional paths, options
• Brown (#CA9161): Neutral elements, helpers

This ensures accessibility for all learners.

Prerequisites

• Python 3.9+ installed (examples use modern Python features)
• Basic programming knowledge (variables, loops, functions in any language)
• Text editor or IDE (VS Code, PyCharm, or any editor)
• Terminal/command prompt access

Install Python from python.org or use your system package manager.

Running Examples

Option 1: Python REPL (Interactive)

python3
>>> # Paste example code here

Option 2: Script File

# Save example to example.py
python3 example.py

Option 3: Jupyter Notebook

pip install jupyter
jupyter notebook
# Create new notebook, paste examples in cells

Learning Strategies

For Java/C# Developers

You’re used to static typing and verbose OOP. Python will feel liberating but initially unfamiliar:

• Dynamic typing: No type declarations required (though type hints are available)
• Duck typing: If it walks like a duck and quacks like a duck, it’s a duck
• No braces: Indentation defines code blocks, whitespace matters

Focus on Examples 1-10 (Python basics) and Examples 40-45 (type hints) to bridge your static typing background.

For JavaScript/TypeScript Developers

You understand dynamic typing and async patterns. Python has similar flexibility:

• Similar feel: Dynamic typing, first-class functions, flexible syntax
• Different async model: async/await works similarly but with different event loop semantics
• No this confusion: Methods receive self explicitly

Focus on Examples 55-65 (asyncio) and Examples 28-35 (decorators) to leverage your JS knowledge.

For C/C++ Developers

You understand systems programming and pointers. Python abstracts all of that:

• No manual memory: Garbage collection handles everything
• No pointers: References are implicit, everything is an object
• Slower but productive: Rapid development, slower execution

Focus on Examples 70-80 (performance optimization, C extensions) to understand when Python’s abstractions matter.

For Ruby Developers

You know dynamic, expressive languages. Python is similar but more explicit:

• Explicit is better: No implicit returns, blocks, or magic methods (mostly)
• One way to do it: Python prefers single obvious solutions
• Significant whitespace: Indentation instead of end keywords

Focus on Examples 35-45 (comprehensions, generators) to see Python’s expressive patterns.

Code-First Philosophy

This tutorial prioritizes working code over theoretical discussion:

• No lengthy prose: Concepts are demonstrated, not explained at length
• Runnable examples: Every example runs in Python REPL or as scripts
• Learn by doing: Understanding comes from running and modifying code
• Pattern recognition: See the same patterns in different contexts across 80 examples

If you prefer narrative explanations, consider the by-concept tutorial (available separately). By-example learning works best when you learn through experimentation.

What You’ll Learn

By completing all 80 examples, you’ll master:

• Python fundamentals: Syntax, types, control flow, functions
• Data structures: Lists, dicts, sets, tuples, and their methods
• Pythonic patterns: Comprehensions, generators, decorators, context managers
• Object-oriented Python: Classes, inheritance, magic methods, protocols
• Functional programming: Lambdas, map/filter/reduce, functools, itertools
• Concurrency: Asyncio, async/await, tasks, and event loops
• Error handling: Exceptions, custom errors, exception chaining
• Testing: Pytest, fixtures, parametrization, mocking
• Type safety: Type hints, protocols, generics, mypy
• Packaging: Modules, packages, virtual environments, pip, setup.py

Navigation

• Beginner - Examples 1-27 (0-40% coverage)
• Intermediate - Examples 28-54 (40-75% coverage)
• Advanced - Examples 55-80 (75-95% coverage)

Ready to learn Python through code? Start with Beginner examples!