Easy State Pattern - support for implementing state machines (Python)

2009-06-15T11:25:17-07:00

Python recipe 576613 by Rodney Drenth (algorithms, decorators, metaclasses, oop, state_machine, state_pattern). Revision 3.

Provides is a module that gives support for implementing state machines. States are implemented as subclasses, derived from the state machine class. Methods that are state dependant or which cause transitions are declared using decorators. Because states can be subclasses of other states, common behaviour among several states is easily supported. The implementation allows for implementing multiple states or substates within a class.

This module best support statem achines implemeting controllers for embedded systems, implementing user interfaces, or in discrete event model simulation. Parsers, which generally have many states and where you would need to define a Transaction method for each different character encountered would be more easily implemented by other means.

Using Metaclasses and Class Decorators to Inherit Function Docstrings (Python)

2011-06-11T00:59:35-07:00

Python recipe 577743 by Eric Snow (decorator, decorators, docstring, inheritance, metaclass, metaclasses). Revision 4.

You'll find three different approaches to copying the method's docstring to the overriding method on a child class.

The function decorator approach is limited by the fact that you have to know the class when you call the decorator, so it can't be used inside a class body. However, recipe #577746 provides a function decorator that does not have this limitation.

dynamically changing encoder (for json) with metaclass (class factory) (Python)

2013-10-24T11:31:44-07:00

Python recipe 578696 by - (class_factory, encode, json, metaclass, metaclasses).

The json.dumps need to be feed with some class (cls =someClass) but what if we want to change the class dynamically? This example can be done by declaring the listOfClasses in class level of course, but the idea is to be changeable. This can be done by the class factory function encoderFacory

Bless Classes into Singletons (Python)

2011-09-21T05:34:52-07:00

Python recipe 577875 by Anand B Pillai (metaclasses, patterns, singleton).

A pattern using metaclasses for "blessing" classes into Singletons.

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