def model_ARIMA(ts, order):
    from statsmodels.tsa.arima_model import ARIMA
    # statsmodel package since version 0.8 strongly recommends to set start_ar_lags.
    # So added it here. Also altered the code to make it robust against compute problems.
    try: 
        model = ARIMA(ts, order = order)
        model_fit = model.fit(disp=0,
                              method='mle',
                              trend='nc',
                              start_ar_lags=7,
                             )
        print(model_fit.summary())
        return(model_fit)
    except ValueError:
        print('This model does not properly compute!')
ar2_model = model_ARIMA(ts_series_ar2, order = (2,0,0))