DI by hand

di_by_hand.py

import abc


class Logger(object):
    __metaclass__ abc.ABCMeta
    
    @abstractmethod
    def log_it(self, message, *args, **kwargs):
        raise NotImplemented
        
        
class FileLogger(Logger):

    def __init__(self, filename):
        self.filename = filename
        
    def log_it(self, message, *args, **kwargs):
        print 'logging to a file'
        
        
class EmailLogger(Logger):

    def __init__(self, emailer):
        self.emailer = emailer
        
    def log_it(self, message, *args, **kwargs):
        print 'logging to an email'


class Emailer(object):

    def __init__(self, server):
        self.server = server
    
    def send(self, message):
        pass
    
        
class DomainObject(object):

    def __init__(self, logger):
        self.logger = logger
        
    def operation(self):
        self.logger.log_it('message')
        
        
d0 = DomainObject(logger=FileLogger('test.log'))
d1 = DomainObject(logger=EmailLogger(Emailer('server'))