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ophyd Kind

Every signal component in an ophyd device carries a Kind attribute that controls how that signal is treated at runtime. It determines whether a signal is included in device.read(), device.read_configuration(), or excluded from both.

Example ophyd device

Example device with signals of different Kind: 

from ophyd import Kind, Device, Component as Cpt, Signal

class MainDevice(Device):
    signal = Cpt(Signal, kind=Kind.normal)
    signal_config = Cpt(Signal, kind=Kind.config)
    signal_omitted = Cpt(Signal, kind=Kind.omitted)

device = MainDevice(name="device")

device.read()
OrderedDict([('device_signal',
          {'value': 0.0, 'timestamp': 1775022455.4195719})])

device.read_configuration()
OrderedDict([('device_signal_config',
          {'value': 0.0, 'timestamp': 1775022455.419599})])

Signals with Kind.omitted are excluded from both device.read() and device.read_configuration(). This is the right choice for internal control handles (triggers, reset commands) and low-level hardware state that is not needed in the data record. These signals can still be accessed directly from the device interface.

Example

device.signal_omitted.read()
{'device_signal_omitted': {'value': 0.0, 'timestamp': 1775022455.4195719}}

The four Kind values

ophyd defines Kind as a flag enumeration in ophyd.Kind. The following values are available:

Kind Integer Meaning
hinted 5 The signal is included in read() and marked as especially important for plotting or analysis.
normal 1 The signal is included in read() and intended for general monitoring. This is the default kind if not specified.
config 2 The signal represents configuration data and is included in read_configuration().
omitted 0 The signal is excluded from both read() and read_configuration().

Combining Kind values

Kind is a flag enum. In practice, this becomes relevant when you have sub-devices in an ophyd device class, because the Kind of the parent component is combined with the Kind of the signals inside that sub-device.

For example, if a sub-device is added with Kind.config, its signals are filtered through that parent Kind. A signal that is Kind.normal inside the sub-device becomes Kind.omitted when viewed from the root device, while a signal that is already Kind.config remains Kind.config.

ophyd device with sub-device 
from ophyd import Kind, Device, Component as Cpt, Signal

class SubDevice(Device):
    sub_signal = Cpt(Signal, kind=Kind.normal)
    sub_config_signal = Cpt(Signal, kind=Kind.config)

class MainDevice(Device):
    signal = Cpt(Signal, kind=Kind.normal)
    signal_config = Cpt(Signal, kind=Kind.config)
    signal_omitted = Cpt(Signal, kind=Kind.omitted)
    sub_device = Cpt(SubDevice, kind=Kind.config)

device = MainDevice(name="device")

device.read()
OrderedDict([('device_signal',
          {'value': 0.0, 'timestamp': 1775022455.4195719})])

device.read_configuration()
OrderedDict([('device_signal_config',
          {'value': 0.0, 'timestamp': 1775022455.419599}),
         ('device_sub_device_sub_config_signal',
          {'value': 0.0, 'timestamp': 1775022455.4196732})])

Kind in BEC

The Kind attribute determines which signals are included in device.read() and device.read_configuration(). To understand when BEC calls these methods during data acquisition, see Readout Priority or the how-to guide on Select a readout priority.