How to use the fbprophet.diagnostics.cross_validation function in fbprophet

"""

    Background:

    This model validation function is still under construction and will be updated during a future release.


    """

    count_of_time_units = len(dates)
    #print(count_of_time_units)
    initial_size = str(int(count_of_time_units * 0.20)) + " days"
    horizon_size = str(int(count_of_time_units * 0.10)) + " days"
    period_size = str(int(count_of_time_units * 0.05)) + " days"

    df_cv = cross_validation(model, initial=initial_size, horizon=horizon_size, period=period_size)
    #df_cv = cross_validation(model,initial='730 days', period='180 days', horizon = '365 days')
    df_p = performance_metrics(df_cv)

    #print(df_cv.head(100))
    #print(df_p.head(100))

    mape_score_avg = str(round(df_p['mape'].mean()*100,2)) + "%"

    return mape_score_avg