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.
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A collection of design patterns and idioms in Python.
|[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)|
|[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 in order to affect outputs|
|[facade](patterns/structural/facade.py)||use one class as an API to a number of others|
|[flyweight](patterns/structural/flyweight.py)||transparently reuse existing instances of objects with similar/identical state|
|[front_controller](patterns/structural/front_controller.py)||single handler requests coming to the application|
|[mvc](patterns/structural/mvc.py)||model<->view<->controller (non-strict relationships)|
|[proxy](patterns/structural/proxy.py)||an object funnels operations to something else|
|[chain_of_responsibility](patterns/behavioral/chain_of_responsibility.py)||apply a chain of successive handlers to try and process the data|
|[catalog](patterns/behavioral/catalog.py)||general methods will call different specialized methods based on construction parameter|
|[chaining_method](patterns/behavioral/chaining_method.py)||continue callback next object method|
|[command](patterns/behavioral/command.py)||bundle a command and arguments to call later|
|[iterator](patterns/behavioral/iterator.py)||traverse a container and access the container's elements|
|[iterator](patterns/behavioral/iterator_alt.py) (alt. impl.)||traverse a container and access the container's elements|
|[mediator](patterns/behavioral/mediator.py)||an object that knows how to connect other objects and act as a proxy|
|[memento](patterns/behavioral/memento.py)||generate an opaque token that can be used to go back to a previous state|
|[observer](patterns/behavioral/observer.py)||provide a callback for notification of events/changes to data|
|[publish_subscribe](patterns/behavioral/publish_subscribe.py)||a source syndicates events/data to 0+ registered listeners|
|[registry](patterns/behavioral/registry.py)||keep track of all subclasses of a given class|
|[specification](patterns/behavioral/specification.py)||business rules can be recombined by chaining the business rules together using boolean logic|
|[state](patterns/behavioral/state.py)||logic is organized into a discrete number of potential states and the next state that can be transitioned to|
|[strategy](patterns/behavioral/strategy.py)||selectable operations over the same data|
|[template](patterns/behavioral/template.py)||an object imposes a structure but takes pluggable components|
|[visitor](patterns/behavioral/visitor.py)||invoke a callback for all items of a collection|
Design for Testability Patterns:
|[dependency_injection](patterns/dependency_injection.py)||3 variants of dependency injection|
|[delegation_pattern](patterns/fundamental/delegation_pattern.py)||an object handles a request by delegating to a second object (the delegate)|
|[blackboard](patterns/other/blackboard.py)||architectural model, assemble different sub-system knowledge to build a solution, AI approach - non gang of four pattern|
|[graph_search](patterns/other/graph_search.py)||graphing algorithms - non gang of four pattern|
|[hsm](patterns/other/hsm/hsm.py)||hierarchical state machine - non gang of four pattern|
When an implementation is added or modified, please review the following guidelines:
All files with example patterns have
### OUTPUT ### section at the bottom
(migration to OUTPUT = """...""" is in progress).
./append_output.sh borg.py) to generate/update it.
Add module level description in form of a docstring with links to corresponding references or other useful information.
Add "Examples in Python ecosystem" section if you know some. It shows how patterns could be applied to real-world problems.
[facade.py](patterns/structural/facade.py) has a good example of detailed description, but sometimes the shorter one as in [template.py](patterns/behavioral/template.py) would suffice.
In some cases class-level docstring with doctest would also help (see [adapter.py](patterns/structural/adapter.py)) but readable OUTPUT section is much better.
Python 2 compatibility
To see Python 2 compatible versions of some patterns please check-out the legacy tag.
When everything else is done - update corresponding part of README.
tox -e ci37 before submitting a patch to be sure your changes will pass CI.
You can also run
pytest commands manually. Examples can be found in
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