example.py

class CLF(object):

        #snip
        
        def handle_cl(self):
                #snip
                if params and params[0]: 
                        self.__input_stream = FileStream(params[0], 'r')
                else:
                        self.__input_stream = IOStream(sys.stdin)
                        
                if self.outfile:
                        self.__output_stream = FileStream(self.outfile, self.output_mode)                       
                else:
                        self.__output_stream = IOStream(sys.stdout)                       
                #snip   
        
        def setup(self):
                #snip
                self.infile = self.__input_stream.get_stream()
                self.outfile = self.__output_stream.get_stream() 

class FileStream(object):

        def __init__(self, filename, mode):
                self.__filename = filename
                self.__mode = mode      
        
        def get_stream(self):
                return open(self.__filename, self.__mode)       

class IOStream(object):

        def __init__(self, stream):
                self.__stream = stream  
        
        def get_stream(self):
                return self.__stream