code: def bill(self, year=None, month=None):
          
          endpoint = '/'.join((self.server_url, '_api', 'v2', 'bill'))
          return self._usage_endpoint(endpoint, year, month)
docs: Retrieves Cloudant billing data, optionally for a given year and month.
  
          :param int year: Year to query against, for example 2014.
              Optional parameter.  Defaults to None.  If used, it must be
              accompanied by ``month``.
          :param int month: Month to query against that must be an integer
              between 1 and 12.  Optional parameter.  Defaults to None.
              If used, it must be accompanied by ``year``.
  
          :returns: Billing data in JSON format