code: def bind_df_model(model_fit, arima_results):
      
      if not hasattr(arima_results, 'df_model'):
          df_model = model_fit.k_exog + model_fit.k_trend + \
              model_fit.k_ar + model_fit.k_ma + \
              model_fit.k_seasonal_ar + model_fit.k_seasonal_ma
          setattr(arima_results, 'df_model', df_model)
docs: Set model degrees of freedom.
  
      Older versions of statsmodels don't handle this issue. Sets the
      model degrees of freedom in place if not already present.
  
      Parameters
      ----------
      model_fit : ARMA, ARIMA or SARIMAX
          The fitted model.
  
      arima_results : ModelResultsWrapper
          The results wrapper.