centipede.py

class Centipede(object):                                                                                         
                                                                                                                 
    def __init__(self):
                                                                                                                 
        self.legs = list()
        self.stomach = list()                                                                                    
    
    def __call__(self, val):                                                                                     
        self.stomach.append(val)                                                                                 
        
    def __str__(self):
        return ",".join(self.stomach)                                                                            
        
    def __setattr__(self, slot, val):                                                                            
    
        if slot in ["legs", "stomach"] and slot not in self.__dict__:                                            
            self.__dict__[slot] = val
        
        elif slot in ["legs", "stomach"] and slot in self.__dict__:                                              
            raise AttributeError("sorry, can not assign {0}".format(slot))
        
        elif slot not in ["legs", "stomach"]:                                                                    
            self.__dict__[slot] = val                                                                            
            self.legs.append(slot)                                                                               
        
        
    def __repr__(self):
      return ",".join(self.legs)