formatters_with_subclasses.py

class Formatter:  
    pass  
      
class DefaultFormatter(Formatter):  
    name = "default"  
    def format(string):  
        return string  
  
class UpperFormatter(Formatter):  
    name = "bar"  
    def format(string):  
        return string.upper()  
                                                                                        
formatters = dict({a.name: a for a in Formatter.__subclasses__()}) 
do_format = lambda string, formatter="default": formatters.get(formatter).format(string)