Merge pull request faif#89 from Ketouem/registry-pattern

Implementing registry pattern

Author: faif

README.md

@@ -37,6 +37,7 @@ Current Patterns:
 |[prototype](prototype.py)| use a factory and clones of a prototype for new instances (if instantiation is expensive) |
 |[proxy](proxy.py)| an object funnels operations to something else |
 |[publish_subscribe](publish_subscribe.py)| a source syndicates events/data to 0+ registered listeners |
+|[registry](registry.py)| keeping track of all subclasses of a given class |
 |[specification](specification.py)| business rules can be recombined by chaining the business rules together using boolean logic |
 |[state](state.py)| logic is org'd into a discrete number of potential states and the next state that can be transitioned to |
 |[strategy](strategy.py)| selectable operations over the same data |

registry.py

@@ -0,0 +1,49 @@
+#!/usr/bin/env python
+# -*- coding: utf-8 -*-
+
+
+classRegistryHolder(type):
+
+REGISTRY={}
+
+def__new__(cls, name, bases, attrs):
+new_cls=type.__new__(cls, name, bases, attrs)
+"""
+ Here the name of the class is used as key but it could be any class
+ parameter.
+ """
+cls.REGISTRY[new_cls.__name__] =new_cls
+returnnew_cls
+
+@classmethod
+defget_registry(cls):
+returndict(cls.REGISTRY)
+
+
+classBaseRegisteredClass(metaclass=RegistryHolder):
+"""
+ Any class that will inherits from BaseRegisteredClass will be included
+ inside the dict RegistryHolder.REGISTRY, the key being the name of the
+ class and the associated value, the class itself.
+ """
+pass
+
+if__name__=="__main__":
+print("Before subclassing: ")
+forkinRegistryHolder.REGISTRY:
+print(k)
+
+classClassRegistree(BaseRegisteredClass):
+
+def__init__(self, *args, **kwargs):
+pass
+print("After subclassing: ")
+forkinRegistryHolder.REGISTRY:
+print(k)
+
+### OUTPUT ###
+# Before subclassing: 
+# BaseRegisteredClass
+# After subclassing: 
+# BaseRegisteredClass
+# ClassRegistree