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.

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	use a generic function with specific factories
borg	a singleton with shared-state among instances
builder	instead of using multiple constructors, builder object receives parameters and returns constructed objects
factory	delegate a specialized function/method to create instances
lazy_evaluation	lazily-evaluated property pattern in Python
pool	preinstantiate and maintain a group of instances of the same type
prototype	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.

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	data<->business logic<->presentation separation (strict relationships)
adapter	adapt one interface to another using a white-list
bridge	a client-provider middleman to soften interface changes
composite