Practical Design Patterns in Python

This project demonstrates the implementation of various design patterns in Python. Each design pattern is implemented conceptually in a file named concept.py and practical examples are provided in files prefixed with ex_. This way you can see how to apply the design pattern in real-world scenarios.

I attempted to use modern Python features and best practices in the examples, such as:

• Type hints
• Dataclasses
• Protocols
• Alternative approaches to design patterns such as function decorators

This repository serves as a comprehensive reference for understanding and implementing design patterns in Python.

What are Design Patterns?

Design patterns are proven solutions to common software design problems. They provide a template for writing code that is maintainable, reusable, and scalable. This project covers a wide range of design patterns, traditionally divided into three categories: creational, structural, and behavioral.

Most of them are from the book "Design Patterns: Elements of Reusable Object-Oriented Software" by Erich Gamma, Richard Helm, Ralph Johnson, and John Vlissides.

Installing

Required Python >= 3.8
Create virtual environment and install dependencies:

py -m venv venv
pip install -r requirements.txt

List of Design Patterns

Each design pattern has at least two scripts:

• concept.py - conceptual implementation
• ex_{script}.py - example real-world scenario

Creational Patterns

• Abstract Factory
  • concept.py
  • ex_gui.py
• Builder
  • concept.py
  • ex_computer.py
  • ex_computer_fluent.py
• Factory Method
  • concept.py
  • ex_notifications.py
• Prototype
  • concept.py
  • ex_documents.py
• Singleton
  • concept.py
  • concept_threadsafe.py
  • ex_configuration.py

Structural Patterns

• Adapter
  • concept_class_adapter.py
  • concept_object_adapter.py
  • ex_xml_to_json_adapter.py
• Bridge
  • concept.py
  • ex_databases.py
  • ex_gui.py
• Composite
  • concept.py
  • ex_file_system.py
• Decorator
  • Class Decorators
    • concept.py
    • ex_data_access.py
  • Classic Decorators
    • concept.py
    • ex_data_access.py
    • ex_data_handler.py
    • ex_document_processor.py
  • Function Decorators
    • concept.py
    • ex_access_control.py
    • ex_caching.py
    • ex_logging.py
• Facade
  • concept.py
  • ex_third_party_lib.py
• Flyweight
  • concept.py
  • ex_chess.py
• Proxy
  • concept.py
  • ex_caching_proxy.py
  • ex_logging_proxy.py
  • ex_protection_proxy.py
  • ex_protection_proxy_decorator.py
  • ex_smart_reference_proxy.py
  • ex_virtual_proxy.py

Behavioral Patterns

• Chain of Responsibility
  • concept.py
  • ex_gui.py
• Command
  • concept.py
  • ex_editor.py
• Iterator
  • concept.py
  • ex_graph.py
  • ex_inventory.py
  • ex_tree.py
• Mediator
  • concept.py
  • ex_chatroom.py
  • ex_stock_market.py
  • ex_ui_components.py
• Memento
  • concept.py
  • ex_game_state.py
  • ex_transactional_db.py
• Observer
  • concept.py
  • concept_distributed.py
  • ex_smart_home.py
  • ex_stock_market.py
• State
  • concept.py
  • ex_traffic_lights_enum.py
  • ex_traffic_lights_sm_library.py
  • ex_traffic_lights_state.py
• Strategy
  • concept.py
  • ex_payment_processor.py
  • ex_text_formatter.py
• Template Method
  • concept.py
  • ex_data_pipeline.py
• Visitor
  • concept.py
  • ex_file_visitor.py

Additional Patterns

• Specification
  • concept.py
  • ex_ecommerce.py

Remarks

• Most of the examples don't do the real job, they just show how you'd leverage the design pattern in certain use case.
  But there are some examples in which I've attempted to do the real job as in bridge pattern database example that uses Testcontainers to boot the real database.
• Whenever possible I've used Protocols as a static way of duck typing (more on that here: Protocols)

References

I recommend these great resources about design patterns

• Design Patterns: Elements of Reusable Object-Oriented Software
• https://refactoring.guru/
• Christopher Okhravi's YT Channel