bootstack.Form#

class bootstack.Form(*, data=None, items=None, col_count=1, min_col_width=275, on_data_change=None, width=None, height=None, accent=None, buttons=None, parent=None, **kwargs)#

Bases: PublicWidgetBase

Data-entry form built from data or explicit field definitions.

Parameters:

  • data (dict[str, Any] | None) – Initial data dict. Keys become field names; types are inferred when items is not provided.

  • items (Sequence[FormItem | Mapping[str, Any]] | None) – Explicit form layout as FieldItem/GroupItem/TabsItem instances or equivalent dicts.

  • col_count (int) – Number of top-level columns. Default 1.

  • min_col_width (int) – Minimum column width in pixels.

  • on_data_change (Callable[[dict[str, Any]], Any] | None) – Callback invoked with the updated data dict on each field change. Equivalent to calling on_data_change() after construction.

  • width (int | None) – Fixed form width in pixels.

  • height (int | None) – Fixed form height in pixels.

  • accent (AccentToken | str | None) – Accent token for the form container.

  • buttons (Sequence[str | DialogButton | dict[str, Any]] | None) – Footer buttons — strings, DialogButton instances, or dicts.

  • parent (Any) – Override the context-stack parent.

  • **kwargs (Any) – Layout placement options applied by the parent container — fill, expand, anchor, margin, row, column, sticky. See Arranging Widgets.

property data: dict[str, Any]#

Current form data dict.

property errors: dict[str, str]#

Current validation errors keyed by field key; empty when all valid.

Read live from the fields’ error signals, so it always reflects the latest validation run.

property is_attached: bool#

Whether the widget is currently placed in its layout.

True while the widget occupies space in its parent; False after detach (or before it has ever been placed). A detached widget keeps its state and can be returned to the layout with attach.

property result: Any#

Value set by button commands.

None until a button is pressed, and None again after a press its command refused — so this always reflects the most recent press that completed, never one that was declined.

property schedule: Schedule#

Scheduler tied to this widget’s lifetime.

All jobs are automatically cancelled when the widget is destroyed. First access creates the Schedule instance; subsequent accesses return the same instance.

Usage:

self.schedule.delay(500, callback)
self.schedule.every(1000, tick)
job = self.schedule.idle(refresh)
job.cancel()
property valid: Signal#

Reactive Signal[bool] — True when every field passes validation.

AND-ed over the fields’ own valid signals and recomputed whenever any field’s validity changes, so a submit button can react to it directly:

form = bs.Form(items=[...])
submit = bs.Button("Save", on_click=save)

def gate(ok):
    submit.disabled = not ok

form.valid.subscribe(gate)

A field is valid until proven otherwise, so this reads True before any rule has run — call validate() to force a full pass (for example, to gate the submit button’s initial state).

property value: dict[str, Any]#

All field values as a dictionary.

attach(**kwargs)#

Return a detached widget to its layout, optionally moving it.

With no arguments, restores the widget to exactly where detach took it from. Any layout kwargs accepted by the original placement (e.g. fill, expand, anchor, sticky, margin) override the stored options. For stacked widgets, index= sets the position among the currently attached siblings (or pass an explicit before=/after= sibling); without one, the snapshotted position is used.

Calling attach on a widget that is already attached moves it (the kwargs are re-applied). Fires on_attach.

Parameters:

**kwargs (Any) – Layout placement options to override for this placement.

Raises:

ParentResolutionError – If the widget was never placed in a layout.

capture(path, *, inset=0, settle=0.1)#

Save a picture of this widget to an image file.

Captures the area this widget occupies on screen — one widget, a whole window, or the entire application, depending on what you call it on. The file extension selects the format, so .png, .jpg, and .pdf all work.

The widget has to be visible. A capture reads pixels from the display, so the window is brought to the front first and a hidden or detached widget cannot be captured at all. Any always-on-top setting the window already had is left as it was found.

Pair it with a save dialog to let the user choose where it goes:

import bootstack as bs

def on_export():
    chosen = bs.ask_save_file(initial_file="dashboard.png")
    if chosen:
        app.capture(chosen)
Parameters:

  • path (str | Path) – Where to write the image. Missing parent folders are created, and the extension chooses the format.

  • inset (int) – Pixels to trim from every edge, zero or more. Use 2 on a whole window to drop the native border artifact.

  • settle (float) – Seconds to let the desktop finish repainting before the pixels are read. The default covers the common case of a dialog closing just beforehand. The interface pauses for this long, so a second click on the control that started the capture waits its turn rather than starting an overlapping one.

Returns:

The path that was written.

Raises:

BootstackError – If the widget is not visible on screen or has been scrolled out of view, if inset is negative, if no capture backend is available, or if the file cannot be written.

Return type:

Path

Added in version 0.3.0.

destroy()#

Destroy the widget and release the resources it holds.

Removes the widget from its parent, destroys its children, and cancels any pending or repeating jobs on its schedule. After this the widget must not be used again. Destroying a container destroys everything inside it.

detach()#

Remove the widget from its layout without destroying it.

The widget stops occupying space but keeps its state, children, and event bindings, ready to be returned with attach. The current position is snapshotted so a plain attach() restores it exactly — for stacked siblings this is the index among the currently attached siblings, so detaching other siblings first shifts that index.

Calling detach on a widget that is already detached, or one that was never placed in a layout, does nothing. Fires on_detach.

emit(event, *, data=None)#

Fire a named event on this widget, as if it produced the event itself.

This is how a composite widget surfaces high-level activity to its listeners, and the generic counterpart to the on_*() shorthands for firing events that have no dedicated method.

It is meant for the framework’s own events — 'change', 'select', 'input' and the rest of the data-carrying names. A handler registered through on() or an on_<event>() shorthand receives what is emitted.

Names that map onto a native event instead ('click', 'focus', 'blur', 'submit', …) are a different matter: emitting one asks the toolkit to deliver a real input event, which carries no payload and can reach handlers the widget installed for its own use. Emitting those is not a way to notify listeners, and a listener bound through on() may not see it. Drive the widget through its properties and methods instead.

Parameters:

  • event (str) – The event name, unprefixed — the same name you pass to on() or an on_<event>() shorthand (e.g. 'change', 'select').

  • data (Any) – The payload delivered to handlers. Pass the matching payload dataclass from bootstack.events — the same object an on_<event>() handler receives.

Example

from bootstack.events import ChangeEvent

field.emit("change", data=ChangeEvent(value=new_value))
field(key)#

Return the Field widget for the given key.

field_signal(key)#

Return the Signal for the named field value.

field_textsignal(key)#

Return the text Signal for the named field.

fields()#

Return all field widgets in insertion order.

get()#

Return all field values as a dictionary.

get_field_value(key)#

Return the current value of the named field.

keys()#

Return all field keys in insertion order.

on(event, handler=None)#

Bind handler to event, or return a composable Stream.

With a handler — binds immediately and returns a Subscription:

sub = widget.on("change", handler)
sub.cancel()

Without a handler — returns a Stream for operator chaining. The Tk binding is created lazily when .listen() is called:

sub = widget.on("change").debounce(300).listen(handler)
sub.cancel()
Parameters:

  • event (str) – Event name (e.g. "change", "click").

  • handler (Callable[[Any], Any] | None) – Optional callback. If omitted, a Stream is returned.

Returns:

Subscription when a handler is provided; Stream otherwise.

Return type:

Stream | Subscription

on_attach(handler=None)#

Register a callback fired when the widget enters the layout.

Fires each time the widget becomes visible in its parent — on initial placement and on every attach. Pair it with on_detach to keep per-visibility resources (timers, observers) tied to the widget’s presence on screen. The handler receives a curated Event.

Parameters:

handler (Callable[[Event], Any] | None) – Called when the widget is attached. Omit to get a composable Stream.

Returns:

A cancellable Subscription when a handler is given, otherwise a Stream.

Return type:

Stream | Subscription

on_data_change() → Stream#
on_data_change(handler: Callable[[dict[str, Any]], Any]) → Subscription

Register a callback fired whenever any field value changes.

The handler receives the current form data as a dict. Called with no handler, returns a composable Stream.

Parameters:

handler (Callable[[dict[str, Any]], Any] | None) – Called with the updated data dict on each field change.

Returns:

Subscription (with handler) or Stream (without handler).

Return type:

Stream | Subscription

on_destroy(handler=None)#

Register a callback fired when the widget is destroyed.

Fires once, as the widget is torn down — the place to release resources the widget owns that aren’t cleaned up automatically (file handles, observers, external subscriptions). The handler receives a curated Event.

Parameters:

handler (Callable[[Event], Any] | None) – Called as the widget is destroyed. Omit to get a composable Stream.

Returns:

A cancellable Subscription when a handler is given, otherwise a Stream.

Return type:

Stream | Subscription

on_detach(handler=None)#

Register a callback fired when the widget leaves the layout.

Fires each time the widget stops occupying space in its parent — on detach and when an ancestor hides it. Pair it with on_attach to release per-visibility resources. The handler receives a curated Event.

Parameters:

handler (Callable[[Event], Any] | None) – Called when the widget is detached. Omit to get a composable Stream.

Returns:

A cancellable Subscription when a handler is given, otherwise a Stream.

Return type:

Stream | Subscription

set(values)#

Set multiple field values from a dictionary.

A partial update — only the keys present in values are written, and keys naming no field are ignored.

set_field_value(key, value)#

Set the value of the named field.

validate()#

Run validation rules; returns True if all fields pass.