class TimestampedModelBase():
   
    def save(self): 
        if not self.id:
            self.created_at = datetime.datetime.today() 
        self.updated_at = datetime.datetime.today()
        models.Model.save(self)

def TimestampedModelInit(model_classes):
        for model_class in model_classes:
            if issubclass(model_class, TimestampedModelBase):
                model_class.add_to_class('created_at', models.DateTimeField(editable=False))
                model_class.add_to_class('updated_at', models.DateTimeField(editable=False))
                model_class.add_to_class('created_by', models.ForeignKey(User))

""" Use: """

class Company(TimestampedModelBase, models.Model):    
    name = models.CharField(maxlength=60)

TimestampedModelInit([Company])