docs: def _sample_item(self, **kwargs):
          """Sample an item from the strata"""
          if 'fixed_stratum' in kwargs:
              stratum_idx = kwargs['fixed_stratum']
          else:
              stratum_idx = None
          if stratum_idx is not None:
              #: Sample in given stratum
              loc = self.strata._sample_in_stratum(stratum_idx,
                                                   replace=self.replace)
          else:
              loc, stratum_idx = self.strata.sample(pmf = self.strata.weights_,
                                                    replace=self.replace)
  
          return loc, 1, {'stratum': stratum_idx}