CMDB.py

# coding=utf-8

class CMDB:
	values, valueHistory, publishers, subscribers = {}, {}, {}, {}

	@staticmethod
	def getValue(id):
		return CMDB.values.get(id, None)

	@staticmethod
	def getValueHistory(id):
		''' happy downloading '''
		return CMDB.valueHistory.get(id, [])
	
	@staticmethod
	def setValue(id, val):
		if id not in CMDB.valueHistory: CMDB.valueHistory[id] = []
		CMDB.valueHistory[id].append(val)
		CMDB.values[id] = val

	@staticmethod
	def getSubscribers(id):
		return CMDB.subscribers.get(id, [])

	@staticmethod
	def addSubscriber(subscriber):
		if id not in CMDB.subscribers: CMDB.subscribers[subscriber.id] = []
		CMDB.subscribers[subscriber.id].append(subscriber)
		return CMDB.getValue(subscriber.id)

	@staticmethod
	def getPublisher(id):
		return CMDB.publishers.get(id, None)

	@staticmethod
	def setPublisher(publisher):
		CMDB.publisher[publisher.id] = publisher

class Ingress:
	def __init__(self, id, f):
		self.id = id
		self.f = f
		print "Links: Registering subscriber for %s" % (self.id)
		value = CMDB.addSubscriber(self)
		print "Links: Last known value for %s is %s" % (self.id, value)

	def update(self, newVal):
		# do a remote call, send a message, write to event journal — whatever... here just call f
		self.f(newVal)
		return True

class Egress:
	def __init__(self, id, initVal):
		self.id = id
		
		self.update(initVal)
			
	def update(self, newVal):
		print "Links: Updating %s: %s —> %s" % (self.id, CMDB.getValue(self.id), newVal)
		CMDB.setValue(self.id, newVal)
		retList = [subscriber.update(newVal) for subscriber in CMDB.getSubscribers(self.id)]
		print "Links: Updated %s %s errors" % (self.id, (False in retList) and "with" or "without")

example.py

# coding=utf-8

from CMDB import Ingress, Egress

class MySQL:
	def __init__(self, connectionString):
		self.connectionString = Egress("database.connectionString", connectionString)

	def updateConnectionString(self, newConnectionString):
		print "MySQL: New connection string is", newConnectionString
		self.connectionString.update(newConnectionString)

class Pohape:
	def __init__(self):
		self.connectionString = Ingress("database.connectionString", self.updateConnectionString)

	def updateConnectionString(self, newConnectionString):
		print "Pohape: database connection string changed to", newConnectionString
		print "Pohape: Recycling"
		return True

mysql = MySQL("jdbc://10.8.0.1")
pohape = Pohape()
mysql.updateConnectionString("jdbc://localhost")

from CMDB import CMDB
print CMDB.getValueHistory("database.connectionString")

example.py output

graven@grace ~/Projects/cobalt » python example.py
Links: Updating database.connectionString: None —> jdbc://10.8.0.1
Links: Updated database.connectionString without errors
Links: Registering subscriber for database.connectionString
Links: Last known value for database.connectionString is jdbc://10.8.0.1
MySQL: New connection string is jdbc://localhost
Links: Updating database.connectionString: jdbc://10.8.0.1 —> jdbc://localhost
Pohape: database connection string changed to jdbc://localhost
Pohape: Recycling
Links: Updated database.connectionString without errors
['jdbc://10.8.0.1', 'jdbc://localhost']