python-patterns

# python-patterns

A collection of design patterns and idioms in Python.

Remember that each pattern has its own trade-offs. And you need to pay attention more to why you're choosing a certain pattern than to how to implement it.

## Creational Patterns

> Patterns that deal with **object creation** — abstracting and controlling how instances are made.

```mermaid
graph LR
    Client -->|requests object| AbstractFactory
    AbstractFactory -->|delegates to| ConcreteFactory
    ConcreteFactory -->|produces| Product

    Builder -->|step-by-step| Director
    Director -->|returns| BuiltObject

    FactoryMethod -->|subclass decides| ConcreteProduct
    Pool -->|reuses| PooledInstance
```

| Pattern | Description |
|:-------:| ----------- |
| [abstract_factory](patterns/creational/abstract_factory.py) | use a generic function with specific factories |
| [borg](patterns/creational/borg.py) | a singleton with shared-state among instances |
| [builder](patterns/creational/builder.py) | instead of using multiple constructors, builder object receives parameters and returns constructed objects |
| [factory](patterns/creational/factory.py) | delegate a specialized function/method to create instances |
| [lazy_evaluation](patterns/creational/lazy_evaluation.py) | lazily-evaluated property pattern in Python |
| [pool](patterns/creational/pool.py) | preinstantiate and maintain a group of instances of the same type |
| [prototype](patterns/creational/prototype.py) | use a factory and clones of a prototype for new instances (if instantiation is expensive) |

## Structural Patterns

> Patterns that define **how classes and objects are composed** to form larger, flexible structures.

```mermaid
graph TD
    Client --> Facade
    Facade --> SubsystemA
    Facade --> SubsystemB
    Facade --> SubsystemC

    Client2 --> Adapter
    Adapter --> LegacyService

    Client3 --> Proxy
    Proxy -->|controls access to| RealSubject

    Component --> Composite
    Composite --> Leaf1
    Composite --> Leaf2
```

|                           Pattern                           | Description                                                                    |
|:-----------------------------------------------------------:|--------------------------------------------------------------------------------|
|           [3-tier](patterns/structural/3-tier.py)           | data<->business logic<->presentation separation (strict relationships)         |
|          [adapter](patterns/structural/adapter.py)          | adapt one interface to another using a white-list                              |
|           [bridge](patterns/structural/bridge.py)           | a client-provider middleman to soften interface changes                        |
|        [composite](patterns/structural/composite.py)        | lets clients treat individual objects and compositions uniformly               |
|        [decorator](patterns/structural/decorator.py)        | wrap functionality with other functionality