README.md

python-patterns

A collection of design patterns and idioms in Python.

When an implementation is added or modified, be sure to update this file and rerun append_output.sh (eg. ./append_output.sh borg.py) to keep the output comments at the bottom up to date.

Current Patterns:

Creational Patterns:

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_method 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:

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 lets clients treat individual objects and compositions uniformly decorator wrap functionality with other functionality in order to affect outputs facade use one class as an API to a number of others flyweight transparently reuse existing instances of objects with similar/identical state front_controller single handler requests coming to the application mvc model<->view<->controller (non-strict relationships) proxy an object funnels operations to something else

Behavioral Patterns:

Pattern Description chain apply a chain of successive handlers to try and process the data catalog general methods will call different specialized methods based on construction parameter chaining_method continue callback next object method command bundle a command and arguments to call later iterator traverse a container and access the container's elements mediator an object that knows how to connect other objects and act as a proxy memento generate an opaque token that can be used to go back to a previous state observer provide a callback for notification of events/changes to data publish_subscribe a source syndicates events/data to 0+ registered listeners registry keep track of all subclasses of a given class specification business rules can be recombined by chaining the business rules together using boolean logic state logic is organized into a discrete number of potential states and the next state that can be transitioned to strategy selectable operations over the same data template an object imposes a structure but takes pluggable components visitor invoke a callback for all items of a collection

Design for Testability Patterns:

Pattern Description setter_injection the client provides the depended-on object to the SUT via the setter injection (implementation variant of dependency injection)

Fundamental Patterns:

Pattern Description delegation_pattern an object handles a request by delegating to a second object (the delegate)

Others:

Pattern Description blackboard architectural model, assemble different sub-system knowledge to build a solution, AI approach - non gang of four pattern graph_search graphing algorithms - non gang of four pattern hsm hierarchical state machine - non gang of four pattern