<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def index_name(self):
 """Get Elasticsearch index name associated to the campaign """

        fmt = self.campaign.export.elasticsearch.index_name
        fields = dict(date=self.report['date'])
        return fmt.format(**fields).lower()