fastcs.attributes.attr_r

Members

AttrIOUpdateCallback	An AttributeIO callback that takes an AttrR and updates its value
AttrOnUpdateCallback	A callback to be called when the value of the attribute is updated
AttrR	A read-only Attribute
AttrUpdateCallback	A callback to be called periodically to update an attribute

fastcs.attributes.attr_r.AttrIOUpdateCallback

An AttributeIO callback that takes an AttrR and updates its value

alias of Callable[[AttrR[DType_T, Any]], Awaitable[None]]

fastcs.attributes.attr_r.AttrUpdateCallback

A callback to be called periodically to update an attribute

alias of Callable[[], Awaitable[None]]

fastcs.attributes.attr_r.AttrOnUpdateCallback

A callback to be called when the value of the attribute is updated

alias of Callable[[DType_T], Awaitable[None]]

class fastcs.attributes.attr_r.AttrR(datatype: DataType[DType_T], io_ref: AttributeIORefT | None = None, group: str | None = None, initial_value: DType_T | None = None, description: str | None = None)

A read-only Attribute

get() → DType_T

Get the cached value of the attribute.

async update(value: Any) → None

Update the value of the attibute

This sets the cached value of the attribute presented in the API. It should generally only be called from an IO or a controller that is updating the value from some underlying source.

Any update callbacks will be called with the new value and any update events with predicates satisfied by the new value will be set.

To request a change to the setpoint of the attribute, use the put method, which will attempt to apply the change to the underlying source.

Parameters:

value – The new value of the attribute

Raises:

ValueError – If the value fails to be validated to DType_T

add_on_update_callback(callback: Callable[[DType_T], Awaitable[None]]) → None

Add a callback to be called when the value of the attribute is updated

The callback will be called with the updated value.

set_update_callback(callback: AttrIOUpdateCallback[DType_T])

Set the callback to update the value of the attribute from the source

The callback will be converted to an async task and called periodically.

bind_update_callback() → Callable[[], Awaitable[None]]

Bind self into the registered IO update callback

async wait_for_predicate(predicate: Callable[[DType_T], bool], *, timeout: float)

Wait for the predicate to be satisfied when called with the current value

Parameters:

• predicate – The predicate to test - a callable that takes the attribute value and returns True if the event should be set

• timeout – The timeout in seconds

async wait_for_value(target_value: DType_T, *, timeout: float)

Wait for self._value to equal the target value

Parameters:

• target_value – The target value to wait for

• timeout – The timeout in seconds

Raises:

TimeoutError – If the attribute does not reach the target value within the timeout