Dependency Injection Hello World in python

di_hello.py

from datetime import *

class ConsoleMessageWriter:
	def __init__(self):
		pass
	
	def write(self, message):
		print message

class LoggedMessageWriter:
	def __init__(self, writer):
		if writer ==  None:
			raise Exception("writer is null")
		self.writer = writer
	
	def write(self,message):
		self.__log(message);
		self.writer.write(message);

	def __log(self, message):
		now = datetime.now()
		print "[INFO] - {:%Y-%m-%d %H:%M:%S} - Writing attempt".format(now)

class PasswordProtectedMessageWriter:

	def __init__(self, writer, password):
		self.__password = password;
		if writer == None:
			raise Exception("writer is null")
		self.writer =  writer
	
	def write(self, message):
		self.__askPassword()
		self.writer.write(message)
	
	def __askPassword(self):
		guessPassword = raw_input("Ultra secure message writer... insert secret password: ")
		if self.__password != guessPassword:
			raise Exception("Wrong password!")
		pass

class MultiChannelWriter:

	def __init__(self, writers):
		self.writers = writers
	
	def write(self, message):
		for writer in self.writers:
			print "\n***"+writer.__class__.__name__+"***"
			try:
				writer.write(message)
			except Exception, e:
				print e.message
			else:
				pass
			finally:
				pass




def main():
	writer = ConsoleMessageWriter()
	loggedWriter = LoggedMessageWriter(writer)
	passwordLoggedWriter = PasswordProtectedMessageWriter(loggedWriter, "secret")

	anotherWriter = ConsoleMessageWriter()
	anotherLoggedWriter = LoggedMessageWriter(writer)

	simpleMessageWriter = ConsoleMessageWriter()

	multichannelWriter = MultiChannelWriter([passwordLoggedWriter, anotherLoggedWriter, simpleMessageWriter])
	multichannelWriter.write("Messaggio")


if __name__ == '__main__':
	main()