Predicate, Condition & Accessor Reference

Prerequisite

This page is a lookup reference. Read Filtering first for explanations of how predicates, conditions, and accessors compose — this page assumes that context.

P (predicates) filter events on the bus. C (conditions) match individual values. A (accessors) extract specific fields from events. All three are top-level imports:

from hassette import P, C, A

Event types: Tables below reference three event types. RawStateChangeEvent fires on entity state changes. CallServiceEvent fires on service calls. HassEvent is the base type for all Home Assistant events.

Key types in signatures: ChangeType is a union of literal value, C.* condition instance, glob string, or callable (value) -> bool. ComparisonCondition is a two-argument callable (old_value, new_value) -> bool — accepts C.Increased, C.Decreased, or a custom function. MISSING_VALUE is a falsy sentinel from hassette.const indicating a field does not exist on the event (distinct from None).

Predicates (P)

A predicate accepts an event and returns bool. Pass predicates to where= on any bus subscription, or compose them with other predicates.

Logic Combinators

Works with: any event type.

Predicate	Signature	Description
P.AllOf	AllOf(predicates: tuple[Predicate, ...])	Returns True when all contained predicates return True.
P.AnyOf	AnyOf(predicates: tuple[Predicate, ...])	Returns True when at least one contained predicate returns True.
P.Not	Not(predicate: Predicate)	Negates the result of the wrapped predicate.
P.Guard	Guard(fn: Predicate[EventT])	Wraps any callable as a typed predicate for use in combinators.

AllOf and AnyOf each have a classmethod ensure_iterable(where) that wraps a single predicate or sequence into the combinator.

Value / Field Matching

Works with: any event type.

Predicate	Signature	Description
P.ValueIs	ValueIs(source: Callable, condition: ChangeType = ANY_VALUE)	Extracts a value via source, then tests it against condition. When condition is ANY_VALUE, always returns True.
P.DidChange	DidChange(source: Callable[..., tuple[Any, Any]])	Returns True when the two values returned by source differ.
P.IsPresent	IsPresent(source: Callable)	Returns True when the value extracted by source is not MISSING_VALUE.
P.IsMissing	IsMissing(source: Callable)	Returns True when the value extracted by source is MISSING_VALUE.

condition accepts a literal value, a C.* condition instance, a glob string, or any callable (value) -> bool.

Entity / Domain / Service Matching

Works with: HassEvent, CallServiceEvent.

Predicate	Signature	Description
P.DomainMatches	DomainMatches(domain: str)	Returns True when the event domain matches domain. Glob patterns are auto-detected.
P.EntityMatches	EntityMatches(entity_id: str)	Returns True when the event entity_id matches. Glob patterns are auto-detected.
P.ServiceMatches	ServiceMatches(service: str)	Returns True when the called service matches. Glob patterns are auto-detected.
P.ServiceDataWhere	ServiceDataWhere(spec: Mapping[str, ChangeType], auto_glob: bool = True)	Returns True when each key in spec satisfies its condition against the event's service_data.

ServiceDataWhere.from_kwargs(*, auto_glob=True, **spec) is an ergonomic constructor for literal keyword arguments:

P.ServiceDataWhere.from_kwargs(entity_id="light.*", brightness=200)

When auto_glob=True (the default), bare glob strings in spec values are automatically wrapped in C.Glob.

State Change Predicates

Works with: RawStateChangeEvent.

Predicate	Signature	Description
P.StateFrom	StateFrom(condition: ChangeType)	Returns True when the old state value satisfies condition.
P.StateTo	StateTo(condition: ChangeType)	Returns True when the new state value satisfies condition.
P.StateComparison	StateComparison(condition: ComparisonCondition)	Returns True when condition(old_state_value, new_state_value) is True. Accepts C.Increased, C.Decreased, or any two-argument callable.
P.StateDidChange	StateDidChange()	Returns True when the state string changed.
P.AttrFrom	AttrFrom(attr_name: str, condition: ChangeType)	Returns True when the named attribute's old value satisfies condition.
P.AttrTo	AttrTo(attr_name: str, condition: ChangeType)	Returns True when the named attribute's new value satisfies condition.
P.AttrComparison	AttrComparison(attr_name: str, condition: ComparisonCondition)	Returns True when condition(old_attr, new_attr) is True for the named attribute.
P.AttrDidChange	AttrDidChange(attr_name: str)	Returns True when the named attribute changed. When old_state is None, returns True if the attribute is present on the new state.

No StateFromTo predicate exists. For from-to matching, combine P.StateFrom and P.StateTo inside P.AllOf:

P.AllOf((P.StateFrom("off"), P.StateTo("on")))

Conditions (C)

A condition is a single-value callable (value) -> bool. Predicates like P.ValueIs accept a condition as their condition argument. The changed_to= and changed_from= subscription helpers also accept conditions directly.

String Matching

Condition	Signature	Description
C.Glob	Glob(pattern: str)	Returns True when the string value matches the glob pattern.
C.StartsWith	StartsWith(prefix: str)	Returns True when the string value starts with prefix.
C.EndsWith	EndsWith(suffix: str)	Returns True when the string value ends with suffix.
C.Contains	Contains(substring: str)	Returns True when the string value contains substring.
C.Regex	Regex(pattern: str)	Returns True when the string value matches the compiled regex pattern.

Collection Membership

Condition	Signature	Description
C.IsIn	IsIn(collection: Sequence[Any])	Returns True when the value is in collection.
C.NotIn	NotIn(collection: Sequence[Any])	Returns True when the value is not in collection.
C.Intersects	Intersects(collection: Sequence[Any])	Returns True when the value (itself a sequence) shares at least one element with collection.
C.NotIntersects	NotIntersects(collection: Sequence[Any])	Returns True when the value (itself a sequence) shares no elements with collection.
C.IsOrContains	IsOrContains(condition: str)	Returns True when the value equals condition, or when the value is a sequence containing it.

collection must be a sequence, not a string. Passing a string raises ValueError.

None / Missing Checks

Condition	Signature	Description
C.IsNone	IsNone()	Returns True when the value is None.
C.IsNotNone	IsNotNone()	Returns True when the value is not None.
C.Present	Present()	Returns True when the value is not MISSING_VALUE.
C.Missing	Missing()	Returns True when the value is MISSING_VALUE.

MISSING_VALUE and None are distinct. C.IsNone / C.IsNotNone test for Python None; C.Present / C.Missing test for Hassette's falsy sentinel that indicates a field does not exist on the event. See Identity Extractors for more on MISSING_VALUE.

Numeric Comparison

Condition	Signature	Description
C.Comparison	Comparison(op: OPS, value: Any)	Returns True when extracted_value op value holds. op is one of ">", "<", ">=", "<=", "==", "!=" (or their spelled-out equivalents "gt", "lt", "ge", "le", "eq", "ne").
C.Increased	Increased()	Two-argument condition. Returns True when float(new) > float(old). For use with P.StateComparison or P.AttrComparison.
C.Decreased	Decreased()	Two-argument condition. Returns True when float(new) < float(old). For use with P.StateComparison or P.AttrComparison.

No C.InRange condition exists. For range checks, combine two C.Comparison instances inside P.AllOf:

P.AllOf((
    P.ValueIs(source=A.get_state_value_new, condition=C.Comparison(">=", 18)),
    P.ValueIs(source=A.get_state_value_new, condition=C.Comparison("<=", 26)),
))

Accessors (A)

An accessor is a factory function that returns a callable (event) -> value. Single-value accessors work with P.ValueIs, P.IsPresent, and P.IsMissing. Tuple-returning accessors (the *_old_new variants) work with P.DidChange. Some accessors are used directly (e.g., A.get_state_value_new); others are factories that require a call first (e.g., A.get_attr_new("brightness")). Bus helpers use accessors internally. Direct use is needed only when pointing a predicate at a non-standard field.

State Value

Works with: RawStateChangeEvent.

Accessor	Returns	Description
A.get_state_value_old	Any \| MISSING_VALUE	The old state string, or MISSING_VALUE when old_state is None.
A.get_state_value_new	Any \| MISSING_VALUE	The new state string, or MISSING_VALUE when new_state is None.
A.get_state_value_old_new	tuple[Any, Any]	(old_state_value, new_state_value) as a tuple.

State Object

Works with: RawStateChangeEvent.

Accessor	Returns	Description
A.get_state_object_old	HassStateDict \| None	The full old state dict, or None when absent.
A.get_state_object_new	HassStateDict \| None	The full new state dict, or None when absent.
A.get_state_object_old_new	tuple[HassStateDict \| None, HassStateDict \| None]	Both state objects as a tuple.

Attribute

Works with: RawStateChangeEvent.

Accessor	Signature	Returns	Description
A.get_attr_old	get_attr_old(name: str)	Any \| MISSING_VALUE	The named attribute from the old state; MISSING_VALUE when absent.
A.get_attr_new	get_attr_new(name: str)	Any \| MISSING_VALUE	The named attribute from the new state; MISSING_VALUE when absent.
A.get_attr_old_new	get_attr_old_new(name: str)	tuple[Any, Any]	(old_attr, new_attr) for the named attribute.
A.get_attrs_old	get_attrs_old(names: list[str])	dict[str, Any]	A dict of the named attributes from the old state. Missing names map to MISSING_VALUE.
A.get_attrs_new	get_attrs_new(names: list[str])	dict[str, Any]	A dict of the named attributes from the new state. Missing names map to MISSING_VALUE.
A.get_attrs_old_new	get_attrs_old_new(names: list[str])	tuple[dict, dict]	Both attribute dicts as a tuple.
A.get_all_attrs_old	get_all_attrs_old	dict[str, Any] \| MISSING_VALUE	All attributes from the old state, or MISSING_VALUE when old_state is None.
A.get_all_attrs_new	get_all_attrs_new	dict[str, Any] \| MISSING_VALUE	All attributes from the new state, or MISSING_VALUE when new_state is None.
A.get_all_attrs_old_new	get_all_attrs_old_new	tuple[dict \| MISSING_VALUE, dict \| MISSING_VALUE]	Both full attribute dicts as a tuple.

Identity

Works with: HassEvent (any event).

Accessor	Returns	Description
A.get_domain	str \| MISSING_VALUE	The domain portion of the event (e.g., "light" from "light.kitchen").
A.get_entity_id	str \| MISSING_VALUE	The entity_id from the event payload, or from service_data for CallServiceEvent.
A.get_context	HassContext	The context dict from the event payload.

Service

Works with: CallServiceEvent.

Accessor	Signature	Returns	Description
A.get_service	get_service	str \| MISSING_VALUE	The service name being called.
A.get_service_data	get_service_data	dict[str, Any] \| MISSING_VALUE	The full service_data dict, or MISSING_VALUE when absent.
A.get_service_data_key	get_service_data_key(key: str)	Any \| MISSING_VALUE	A specific key from service_data; MISSING_VALUE when absent.

Other

Accessor	Signature	Returns	Description
A.get_path	get_path(path: str)	Any \| MISSING_VALUE	Extracts a nested value by dot-separated path (e.g., "new_state.attributes.brightness"); MISSING_VALUE on any access failure.
A.get_all_changes	get_all_changes(exclude: Sequence[str] = DEFAULT_EXCLUDE)	dict[str, Any]	A recursive diff between old and new state, mapping changed keys to (old_value, new_value). Excludes last_reported, last_updated, last_changed, and context by default.

get_path works with any event type. get_all_changes works with RawStateChangeEvent.

For writing custom accessors, see Custom Extractors.

See Also

• Filtering. How predicates, conditions, and accessors compose in practice.
• Custom Extractors. Writing accessors for non-standard event fields.