code: def get_margin_balance(self, symbol=None, _async=False):
          
          params = {}
          path = '/v1/margin/accounts/balance'
          if symbol:
              params['symbol'] = symbol
  
          return api_key_get(params, path, _async=_async)
docs: 借贷账户详情,支持查询单个币种
          :param symbol:
          :return: