'Returns a list of tags to be used when recording metrics about this model.
Each field named in ``self.metric_tag_fields`` is used as a tag value,
under the key ``<class>.<metric_field>``. The tag model_class is used to
record the class name of the model.'

@property
def _metric_tags(self):

    tags = [u'{}.{}:{}'.format(self.__class__.__name__, attr, self[attr]) for attr in self.metric_tag_fields if (attr in self.attributes)]
    tags.append(u'model_class:{}'.format(self.__class__.__name__))
    return tags
