# Sending notifications

Tryton embeds a bus system allowing the system to send text messages to clients logged in the system.

It allows the server to warn quickly the client user about some events using the `notify()` function. Sending the notifications is done in a transactional way and will occur at then end of the transaction.

For example, we warn the user of low stock level when selecting a product:

    from trytond.bus import notify

    class SaleLine:
        __name__ = 'sale.line'

        def on_change_product(self):
            super().on_change_product()
            if compute_stock(self.product) < 0:
                notify('Not enough stock', priority=3)