An alternative to doing switches in OOP

interfaces.py

#!/usr/bin/env python

"""
Based on the this SO question:
http://stackoverflow.com/questions/126409/ways-to-eliminate-switch-in-code

Ways to use object oriented programming to create interfaces
instead of using switch patterns like:
	if 
	elif
	elif
	...
	else

The main logic does not contain any knowledge of what to do with different
cases. Its up to the implementations to handle the actions through a common
interface.


Justin Israel
[email protected]
justinfx.com

"""


import os
import sys

class AbstractInterface(object):
	"""
	AbstractInterface

	This class is meant to be subclasses, and not
	used directly. Subclasses should impliment the
	methods of this class.

	"""
	def getFullPath(self, afile):
		pass
	
	def numThreads(self):
		pass


class Posix(AbstractInterface):
	"""
	Implements the AbstractInterface for Posix systems
	"""
	def getFullPath(self, aFile):
		return os.path.join( "/home/blah/food", aFile)
	
	def numThreads(self):
		# call out to the filesystem with specific
		# posix commands to determine how many cpus
		# or threads?
		return 8


class Nt(AbstractInterface):
	"""
	Implements the AbstractInterface for Nt systems
	"""
	def getFullPath(self, aFile):
		return os.path.join(r'Z:\path\to\root', aFile)
	
	def numThreads(self):
		# call out to the filesystem with specific
		# posix commands to determine how many cpus
		# or threads?
		return 2

def main():


	systems = {
		'nt': Nt(),
		'posix': Posix()
	}

	try:
		system = systems[os.name]
	except KeyError:
		print "System not supported!"
		sys.exit(1)

	print system.getFullPath('myFile.txt')
	print system.numThreads()


if __name__ == "__main__":
	main()