yaq and happi

Happi (Heuristic Access to Positioning of Photon Instrumentation), is a Python package developed at the Linac Coherent Light Source. Happi is part of the Bluesky ecosystem.

Happi provides an interface for discovering hardware interfaces. Despite the name containing "photon", Happi's interface is generic. It's somewhat like a database for Bluesky interface objects. Tools like Typhos can automatically use Happi to discover what hardware is avaliable on a given machine.

yaq integrates with Happi via the yaqc-bluesky package. yaq users may add yaqc-bluesky instances to the Happi database. Importantly, yaqc-bluesky instances exist seamlessly in Happi alongside other Bluesky interface providers.


We recommend using Happi's JSON backend in user data directory. Here's how to make a Happi client using this path.

import appdirs
import pathlib
import happi

# make happi client
db_path = pathlib.Path(appdirs.user_data_dir("happi")) / "db.json"
happi_backend = happi.backends.backend(db_path)
happi_client = happi.Client(database=happi_backend)

We'll be using this as our backend example for the rest of this discussion. Of-course any Happi-supported backend will work, see Happi's documentation on selecting a backend.


Let's add a new yaqc-bluesky instance to Happi. In this case we have a daemon locally at port 38500.

>>> import yaqc_bluesky
>>> item = yaqc_bluesky.happi_containers.YAQItem(name="test", port=38500)
>>> happi_client.add_device(item)


Once a device has been added to Happi we can search for it.

>>> happi_client.find_device(name="test")


Loading gives back the yaqc-bluesky device itself.

>>> happi_client.load_device(name="test")
<yaqc_bluesky._device.YAQDevice object at 0x7f227963e790>

built 2021-01-12 19:45:12                                      CC0: no copyright