A collection of design patterns implemented (by other people) in python
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.gitignore
.travis.yml
3-tier.py
README.md
__init__.py
abstract_factory.py
adapter.py
append_output.sh
borg.py
bridge.py
builder.py
catalog.py
chain.py
chaining_method.py
command.py
composite.py
decorator.py
delegation_pattern.py
facade.py
factory_method.py
flyweight.py
front_controller.py
graph_search.py
hsm.py
iterator.py
lazy_evaluation.py
mediator.py
memento.py
mvc.py
observer.py
pool.py
prototype.py
proxy.py
publish_subscribe.py
registry.py
run_all.sh
specification.py
state.py
strategy.py
template.py
test_abstract_factory.py
test_adapter.py
test_borg.py
test_bridge.py
test_command.py
test_flyweight.py
test_hsm.py
test_observer.py
test_proxy.py
test_publish_subscribe.py
test_state.py
test_strategy.py
visitor.py

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 encapsulate and provide access to a number of different objects
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
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

Others:

Pattern Description
graph_search (graphing algorithms, not design patterns)