Special Reference Objects

When you refer to one or more devices, you supply a reference to the sender. This can be a single serial like "d073d5006677", a list of these serials; or an object that knows how to search for devices based on some condition.


The serial is the MAC address of the device and can be found printed on the side of the device. It is a 12 character hex number that starts with d073d5. So d073d5xxxxxx, like d073d50a3bcd.

You can also target devices by setting the serial directly on the packets:

from photons_messages import DeviceMessages, LightMessages

async def my_action(target):
    # Get color for d073d5000001
    get_color = LightMessages.GetColor(target="d073d5000001")

    # Get power messages for for d073d5000002 and d073d5000003
    get_power1 = DeviceMessages.GetPower(target="d073d5000002")
    get_power2 = DeviceMessages.GetPower(target="d073d5000003")

    async with target.session() as sender:
        async with pkt in sender([get_color, get_power1, get_power2]):
            if pkt | LightMessages.LightState:
                assert pkt.serial == "d073d5000001"

            elif pkt | DeviceMessages.StatePower:
                assert pkt.serial in ("d073d5000002", "d073d5000003")

Otherwise you can use one of the following objects to address your devices in either the sender or in manually discovering serials.


This doesn’t take in any arguments and just performs a normal discovery to find all the devices on the network.


Broadcasting on a network can be unreliable and doesn’t necessarily return all the devices that are actually on the network.


This takes in a single serial "d073d5000001" or a list of serials. It will keep searching for the serials you ask for until either the timeout occurs or it finds all the devices.


This takes in the path to a file that has one serial per line. It will then create a HardCodedSerials reference and use that to discover those devices.


This allows you to find devices based on their attributes. You can find more information about this on the page about the DeviceFinder

Making your own finder

A SpecialReference is an object that has the following three methods on it:

from photons_app.errors import DevicesNotFound

import binascii

class MyReference:
    See below for the easy way of creating one of these
    async def find(sender, *, timeout, **kwargs):
        # serials is a list of serials
        serials = [serial1, serial2, ...]

        # found is a dictionary of target bytes to transport information.
        # The easiest way to get this is
        # ```
        #    targets = [binascii.unhexlify(serial)[:6] for serial in serials]
        #    found = {target: sender.found[target] for serial in targets}
        # ```

        return found, serials

    def reset(selt):
        # Clear any cached data

    def raise_on_missing(self, found):
        # If the found dictionary doesn't contain all the serials we
        # expect, then raise a DevicesNotFound
        raise DevicesNotFound(missing=[missing_serial1, ...])

The easiest way to create one of these objects is to inherit from photons_app.special.SpecialReference and implement the find_serials method:

from photons_app.errors import DevicesNotFound

from photons_transport import RetryTicker

import binascii

class UpTo(SpecialReference):
    A SpecialReference object that finds the first ``upto`` devices

    def __init__(self, upto=5):
        self.upto = upto

    async def find_serials(self, sender, *, timeout, broadcast=True):
        found = getattr(sender, "found", {})
        serials = []

        # Just keep retrying every 0.5 seconds until it's been 2 seconds,
        # And then retry every second after that.
        retrier = RetryTicker(timeouts=[[0.5, 2], [1, 2]])

        async for time_left, _ in retrier.tick(sender.stop_fut, timeout):
            if len(serials) >= self.upto:

            _, ss = await sender.find_devices(
                timeout=time_left, broadcast=broadcast, raise_on_none=False

            for s in ss:
                if s not in serials:
                    if len(serials) >= self.upto:


                    target = binascii.unhexlify(s)[:6]
                    found[target] = sender.found[target]

        # Only need to return the found dictionary
        # I create a serials array anyway to avoid unhexlifying serials
        # Every time sender.find_devices returns.
        return found

    # If we knew specific serials, we could do
    # ```
    #    def missing(self, found):
    #       # Say we didn't find d073d5000001 despite wanting it
    #       return ["d03d5000001"]
    # ```

Then you would say:

from photons_messages import DeviceMessages

async def my_action(target):
    # Turn off up to the first 6 devices I find
    async with target.session() as sender:
        await sender(DeviceMessages(level=0), UpTo(6))