code: def get_class_field(cls, field_name):
          
          if not cls.has_field(field_name):
              raise AttributeError('"%s" is not a field for the model "%s"' %
                                   (field_name, cls.__name__))
  
          field = getattr(cls, '_redis_attr_%s' % field_name)
  
          return field
docs: Return the field object with the given name (for the class, the fields
          are in the "_redis_attr_%s" form)