How to use the broker.Broker.is_trade_closed function in broker

def _babysit(self):
        """ (See strategy.py for documentation) """
        Log.write('fifty.py babysit(): _open_tade_ids: {}'.format(self.open_trade_ids))

        for open_trade_id in self.open_trade_ids:
            is_closed = Broker.is_trade_closed(open_trade_id)
            if is_closed[0]:
                Log.write('"fifty.py" _babysit(): Trade ({}) has closed with reason: {}'
                    .format( open_trade_id, str(is_closed[1]) )
                )
                # If SL hit, reverse direction.
                if is_closed[1] == TradeClosedReason.STOP_LOSS_ORDER:
                    if self.go_long:
                        self.go_long = False
                    else:
                        self.go_long = True
                self.open_trade_ids.remove(open_trade_id)
            else:
                trade = Broker.get_trade(open_trade_id)
                instrument = trade.instrument
                sl = round( float(trade.stop_loss), 2 )
                go_long = int(trade.units) > 0

instrument = trade.instrument
                sl = round( float(trade.stop_loss), 2 )
                go_long = int(trade.units) > 0

                if go_long: # currently long
                    cur_bid = Broker.get_bid(instrument)
                    if cur_bid != None:
                        if cur_bid - sl > self.sl_price_diff:
                            new_sl = cur_bid - self.sl_price_diff
                            resp = Broker.modify_trade(
                                trade_id=open_trade_id,
                                stop_loss_price=str(round(new_sl, 2))
                            )
                            if resp == None:
                                Log.write('"fifty.py" _babysit(): Modify failed. Checking if trade is closed.')
                                closed = Broker.is_trade_closed(open_trade_id)
                                Log.write('fifty.py babysit(): is_trade_closed returned:\n{}'.format(closed))
                                if closed[0]:
                                    Log.write('"fifty.py" _babysit(): BUY trade has closed. (BUY)')
                                    self.open_trade_ids.remove(open_trade_id)
                                    # If SL hit, reverse direction.
                                    if closed[1] == TradeClosedReason.STOP_LOSS_ORDER:
                                        self.go_long = False
                                else:
                                    Log.write('"fifty.py" _babysit(): Failed to modify BUY trade.')
                                    raise Exception
                            else:                                       
                                Log.write('"fifty.py" _babysit(): Modified BUY trade with ID (',\
                                     open_trade_id, ').')
                    else:
                        Log.write('"fifty.py" _babysit(): Failed to get bid while babysitting.')
                        raise Exception

Log.write('"fifty.py" _babysit(): Modified BUY trade with ID (',\
                                     open_trade_id, ').')
                    else:
                        Log.write('"fifty.py" _babysit(): Failed to get bid while babysitting.')
                        raise Exception
                else: # currently short
                    cur_bid = Broker.get_bid(instrument)
                    if cur_bid != None:
                        if sl - cur_bid > self.sl_price_diff:
                            new_sl = cur_bid + self.sl_price_diff
                            resp = Broker.modify_trade(
                                trade_id=open_trade_id, 
                                stop_loss_price=str(round(new_sl, 2))
                            )
                            if resp == None:
                                closed = Broker.is_trade_closed(open_trade_id)
                                Log.write('fifty.py babysit(): is_trade_closed returned:\n{}'.format(closed))
                                if closed[0]:
                                    Log.write('"fifty.py" _babysit(): SELL trade has closed. (BUY)')
                                    self.open_trade_ids.remove(open_trade_id)
                                    # If SL hit, reverse direction.
                                    if closed[1] == TradeClosedReason.STOP_LOSS_ORDER:
                                        self.go_long = True
                                else:
                                    Log.write('"fifty.py" in _babysit(): Failed to modify SELL trade.')
                                    raise Exception
                            else:
                                Log.write('"fifty.py" _babysit(): Modified SELL trade with ID (',\
                                    open_trade_id, ').')
                    else:
                        Log.write('"fifty.py" _babysit(): Failed to get ask while babysitting.')
                        raise Exception

# Delete any trades from the database that are no longer open.
        #   First, ignore trades that the broker has open.
        db_trades = DB.execute('SELECT trade_id FROM open_trades_live')
        Log.write('"daemon.py" recover_trades():\ndb open trades: {}\nbroker open trades: {}'
            .format(db_trades, open_trades_broker))
        for index, dbt in enumerate(db_trades): # O(n^3)
            for otb in open_trades_broker:
                if str(dbt[0]) == str(otb.trade_id): # compare trade_id
                    del db_trades[index]
        #   The remaining trades are in the "open trades" db table, but 
        #   the broker is not listing them as open.
        #   They may have closed since the daemon last ran; confirm this.
        #   Another cause is that trades are automatically removed from
        #   Oanda's history after much time passes.
        for dbt in db_trades:
            if Broker.is_trade_closed(dbt[0])[0]:
                # Trade is definitely closed; update db.
                Log.write('"daemon.py" recover_trades(): Trade {} is closed. Deleting from db.'
                    .format(dbt[0]))
            else:
                # Trade is in "open trades" db table and the broker
                # says the trade is neither open nor closed.
                DB.bug('Trade w/ID ({}) is neither open nor closed.'
                    .format(dbt[0]))
                Log.write('"daemon.py" recover_trades(): Trade w/ID (',
                    '{}) is neither open nor closed.'.format(dbt[0]))
            DB.execute('DELETE FROM open_trades_live WHERE trade_id="{}"'
                .format(dbt[0]))
            
        """
        Fill in info not provided by the broker, e.g.
        the name of the strategy that opened the trade.