How to use the prophet.exceptions.ProphetException function in prophet

before the start date
            slippage (float): Percent price slippage when executing order
            commission (float): Amount of commission paid per order
            cash (int): Amount of starting cash
            portfolio (prophet.portfolio.Portfolio): Starting portfolio

        Return:
            prophet.backtest.BackTest
        """
        # Setup
        if not end:
            today = dt.date.today()
            end = dt.datetime.combine(today, dt.time())

        if not self._order_generator:
            raise ProphetException("Must set an order generator by calling"
                                   "set_order_generator.")

        timestamps = trading_days[(trading_days >= start) &
                                  (trading_days <= end)]
        effective_start = timestamps[0]

        data = self._generate_data(start=effective_start,
                                   end=end,
                                   lookback=lookback)

        # Run backtest
        return backtest(cash=cash,
                        data=data,
                        start=effective_start,
                        end=end,
                        slippage=slippage,

generate orders for.
            lookback (int): Number of trading days you want data for before the
                (target_datetime - buffer_days)
            cash (int): Amount of starting cash
            buffer_days (int): number of trading days you want extra data
                generated for. Acts as a data start date.
            portfolio (prophet.portfolio.Portfolio): Starting portfolio
        """
        target_datetime_index = trading_days.get_loc(target_datetime)
        start = trading_days[target_datetime_index - buffer_days]
        data = self._generate_data(start,
                                   target_datetime,
                                   lookback)
        prices = data.get('prices')
        if prices is None:
            raise ProphetException("Price data is required to run a backtest. "
                                   "Please add a data generator with the name "
                                   "property set to 'prices'.")
        return self._order_generator.run(prices=prices,
                                         data=data,
                                         timestamp=target_datetime,
                                         cash=cash,
                                         portfolio=portfolio)

cache_filename = "{stock}-{start}-{end}.csv".format(
                stock=symbol_path, start=data_start, end=end
            ).replace(':', '-')
            cache_filepath = self.get_cache_filepath(cache_filename)
            if os.path.exists(cache_filepath):
                symbol_data = pd.DataFrame.from_csv(cache_filepath)
            else:
                symbol_data = pdr.DataReader(symbol, source,
                                             data_start, end).sort_index()
                symbol_data.to_csv(cache_filepath)
            symbols_data[symbol] = symbol_data

        symbols_panel = pd.concat(symbols_data).to_panel()
        symbols_panel = symbols_panel.swapaxes('minor', 'major')
        if symbols_panel.empty:
            ProphetException("No data for the range specified:"
                             " %s to %s" % (data_start, end))

        symbols_panel = symbols_panel.fillna(method='ffill')
        symbols_panel = symbols_panel.fillna(method='bfill')
        symbols_panel = symbols_panel.fillna(1.0)
        return symbols_panel.loc[:, ((symbols_panel.major_axis >= data_start)
                                     & (symbols_panel.major_axis <= end))]