async def fetch_closed_orders(self, symbol=None, since=None, limit=None, params={}):
    orders = (await self.fetch_orders(symbol, since, limit, params))
    return self.filter_by(orders, 'status', 'closed')
async def fetch_closed_orders(self, symbol=None, since=None, limit=None, params={}):
    orders = (await self.fetch_orders(symbol, since, limit, params))
    return self.filter_by(orders, 'status', 'closed')