def __init__(self, exchange: 'Exchange', quantity: 'Quantity'):
    self._exchange = exchange
    self._instrument = quantity.instrument
    self._balance = quantity
    self._locked = {}
def __init__(self, exchange: 'Exchange', quantity: 'Quantity'):
    self._exchange = exchange
    self._instrument = quantity.instrument
    self._balance = quantity
    self._locked = {}