When and how to execute the first an only trade in a buy-and-hold strategy

Stefan Krecher

Hi
I'm using a BuyAndHold strategy to compare the results of a strategy that I'm developing.
I'd like to calculate the maximum number of stocks that I'm able to buy, based on the current price and the available cash:

class BuyAndHold(bt.Strategy):
    def start(self):
        self.val_start = self.broker.get_cash()  # keep the starting cash

    def nextstart(self):
        # Buy all the available cash
        size = int(self.broker.get_cash() / self.data)
        print("nextstart price %.2f size=%s" % (float(10000.0 / float(self.broker.get_cash() / self.data)), size))
        self.buy(size=size)

Output of the above is:
nextstart price 12.96 size=771

size is calculated based on the closing price of the very first entry in the dataset.

But the buy-order in the "nextstart" function will not be executed.
By playing around with different sizes, I found out that self.buy will be executed with a number of 751 (instead of the calculated number of 771).
When I divide 10000 by the opening price of the second candle in the dataset - I'll get the correct number of shares (751) that I'm allowed to buy in the nextstart function.
So what am I missing here? Assuming that "nextstart" is the place to execute the very first trade of the strategy, I would need to get the opening-price of the second entry in the dataset. But how?
Or is this a bug? If I would like to buy at the very first possible point in time, I should see the opening price of the very first candle.

Looking forward to any suggestions.

ab_trader

def next(self):
    if not self.position:
        self.buy()

ab_trader

@Stefan-Krecher said in When and how to execute the first an only trade in a buy-and-hold strategy:

So what am I missing here?

bt executes the orders on the next bar open price since this is the next available price after the order is issued in the next() or nextstart().