https://github.com/tokoroten-lab/joycon-python/blob/051f5fc6ff0c6252c997dd58d7ff35f58ab28c91/pyjoycon/joycon.py#L43
when I connect two pairs of joycon, some joycon read wrong number.
Maybe
self._joycon_device = self._open(vendor_id, product_id, serial=self.serial)
rather than
self._joycon_device = self._open(vendor_id, product_id, serial=None)