'Removes all given orders from the blotter\'s open_orders list.
Parameters
closed_orders: iterable of orders that are closed.
Returns
None'

def prune_orders(self, closed_orders):

    for order in closed_orders:
        asset = order.asset
        asset_orders = self.open_orders[asset]
        try:
            asset_orders.remove(order)
        except ValueError:
            continue
    for asset in list(self.open_orders.keys()):
        if (len(self.open_orders[asset]) == 0):
            del self.open_orders[asset]
