code: def _build_calmar_data(self):
          
          # Select only filtered entities
          assert self.initial_weight_name is not None
          data = pd.DataFrame()
          data[self.initial_weight_name] = self.initial_weight * self.filter_by
          for variable in self.margins_by_variable:
              if variable == 'total_population':
                  continue
              assert variable in self.survey_scenario.tax_benefit_system.variables
              period = self.period
              data[variable] = self.survey_scenario.calculate_variable(variable = variable, period = period)
  
          return data
docs: Builds the data dictionnary used as calmar input argument