Buying and selling with Alpaca

martingale.py

import alpaca_trade_api as tradeapi

class MartingaleTrader(object):
    def __init__(self):
        # API authentication keys can be taken from the Alpaca dashboard.
        # https://app.alpaca.markets/paper/dashboard/overview
        self.key_id = "REPLACE_ME"
        self.secret_key = "REPLACE_ME"
        self.base_url = 'https://paper-api.alpaca.markets'

        # The symbol we will be trading
        self.symbol = 'SPY'

        # When this variable is not None, we have an order open
        self.current_order = None

        # The closing price of the last aggregate we saw
        self.last_price = 0

        # The connection to the Alpaca API
        self.api = tradeapi.REST(
            self.key_id,
            self.secret_key,
            self.base_url
        )
        
        # Get our starting position, in case we already have one open
        try:
            self.position = int(self.api.get_position(self.symbol).qty)
        except:
            # No position exists
            self.position = 0


    def send_order(self, target_qty):
        # We don't want to have two orders open at once
        if self.current_order is not None:
            self.api.cancel_order(self.current_order.id)

        delta = target_qty - self.position
        if delta == 0:
            return
        print(f'Ordering towards {target_qty}...')
        try:
            if delta > 0:
                buy_qty = delta
                if self.position < 0:
                    buy_qty = min(abs(self.position), buy_qty)
                print(f'Buying {buy_qty} shares.')
                self.current_order = self.api.submit_order(
                    self.symbol, buy_qty, 'buy',
                    'limit', 'day', self.last_price
                )
            elif delta < 0:
                sell_qty = abs(delta)
                if self.position > 0:
                    sell_qty = min(abs(self.position), sell_qty)
                print(f'Selling {sell_qty} shares.')
                self.current_order = self.api.submit_order(
                    self.symbol, sell_qty, 'sell',
                    'limit', 'day', self.last_price
                )
        except Exception as e:
            print(e)


if __name__ == '__main__':
    trader = MartingaleTrader()
    # Order five shares
    trader.send_order(5)