textual.reactive

This module contains the Reactive class which implements reactivity.

Initialize

Initialize(callback)

Bases: Generic[ReactiveType]

Initialize a reactive by calling a method parent object.

Example

    class InitializeApp(App):

        def get_names(self) -> list[str]:
            return ["foo", "bar", "baz"]

        # The `names` property will call `get_names` to get its default when first referenced.
        names = reactive(Initialize(get_names))

Reactive

Reactive(
    default,
    *,
    layout=False,
    repaint=True,
    init=False,
    always_update=False,
    compute=True,
    recompose=False,
    bindings=False,
    toggle_class=None
)

Bases: Generic[ReactiveType]

Reactive descriptor.

Parameters:

Name	Type	Description	Default
default	ReactiveType | Callable[[], ReactiveType] | Initialize[ReactiveType]	A default value or callable that returns a default.	required
layout	bool	Perform a layout on change.	False
repaint	bool	Perform a repaint on change.	True
init	bool	Call watchers on initialize (post mount).	False
always_update	bool	Call watchers even when the new value equals the old value.	False
compute	bool	Run compute methods when attribute is changed.	True
recompose	bool	Compose the widget again when the attribute changes.	False
bindings	bool	Refresh bindings when the reactive changes.	False
toggle_class	str | None	An optional TCSS classname(s) to toggle based on the truthiness of the value.	None

owner property

owner: Type[MessageTarget]

The owner (class) where the reactive was declared.

ReactiveError

Bases: Exception

Base class for reactive errors.

TooManyComputesError

Bases: ReactiveError

Raised when an attribute has public and private compute methods.

reactive

reactive(
    default,
    *,
    layout=False,
    repaint=True,
    init=True,
    always_update=False,
    recompose=False,
    bindings=False,
    toggle_class=None
)

Bases: Reactive[ReactiveType]

Create a reactive attribute.

Parameters:

Name	Type	Description	Default
default	ReactiveType | Callable[[], ReactiveType] | Initialize[ReactiveType]	A default value or callable that returns a default.	required
layout	bool	Perform a layout on change.	False
repaint	bool	Perform a repaint on change.	True
init	bool	Call watchers on initialize (post mount).	True
always_update	bool	Call watchers even when the new value equals the old value.	False
recompose	bool	Compose the widget again when the attribute changes.	False
bindings	bool	Refresh bindings when the reactive changes.	False
toggle_class	str | None	An optional TCSS classname(s) to toggle based on the truthiness of the value.	None

var

var(
    default,
    init=True,
    always_update=False,
    bindings=False,
    toggle_class=None,
)

Bases: Reactive[ReactiveType]

Create a reactive attribute (with no auto-refresh).

Parameters:

Name	Type	Description	Default
default	ReactiveType | Callable[[], ReactiveType] | Initialize[ReactiveType]	A default value or callable that returns a default.	required
init	bool	Call watchers on initialize (post mount).	True
always_update	bool	Call watchers even when the new value equals the old value.	False
bindings	bool	Refresh bindings when the reactive changes.	False
toggle_class	str | None	An optional TCSS classname(s) to toggle based on the truthiness of the value.	None

await_watcher async

await_watcher(obj, awaitable)

Coroutine to await an awaitable returned from a watcher

invoke_watcher

invoke_watcher(
    watcher_object, watch_function, old_value, value
)

Invoke a watch function.

Parameters:

Name	Type	Description	Default
watcher_object	Reactable	The object watching for the changes.	required
watch_function	WatchCallbackType	A watch function, which may be sync or async.	required
old_value	object	The old value of the attribute.	required
value	object	The new value of the attribute.	required