Architecture

Puppeteer and Puppet

genro-textual follows a strict separation between configuration and execution:

  • TextualApp (puppeteer) — extends BagAppBase. Owns recipe, data, builder, compiler, binding. Creates and drives the LiveApp.

  • LiveApp (puppet) — extends textual.app.App. No logic of its own. Built and controlled by the puppeteer.

  • CompiledBag — the script. Produced by the compiler, kept in sync by BindingManager.

Pipeline

        graph TD
    R[recipe] --> SB[Source Bag]
    SB -->|compile| CB[Compiled Bag]
    CB -->|render| WT[Widget Tree]
    DB[Data Bag] -->|"binding (data → widget)"| CB
    WT -->|"blur/change (widget → data)"| DB

Single-Pass Compilation

The compiler walks the source Bag once. For each node:

  1. Clean subscription map for this subtree

  2. Expand component if resolver present

  3. Create node in compiled Bag

  4. Resolve ^pointers against data and register in subscription map

  5. Recurse into children

Subscription Map

Flat str → list[str]:

{
    "form.name": ["horizontal_0.verticalscroll_0.input_0?value",
                   "horizontal_0.verticalscroll_0.static_2"],
}

Key: data path. Value: compiled node paths (with optional ?attr suffix).

Modules

textual_builder.py

TextualWidgetsMixin + TextualBuilder(TextualWidgetsMixin, BagBuilderBase)

All @element and @component definitions live in the mixin for inheritance via MRO.

Elements include:

  • Containers: vertical, horizontal, grid, center, etc.

  • Widgets: static, button, input, checkbox, datatable, tree (with store), etc.

  • App config: css, binding (not rendered as widgets)

  • Components: fieldset, form (expanded at compile time)

textual_compiler.py

TextualCompiler(BagCompilerBase)

Inherits compile() from base (single-pass: expand + resolve + register). Defines its own render(compiled_bag, live_app):

  1. Extract css nodes → apply to live_app.stylesheet

  2. Extract binding nodes → call live_app.bind()

  3. Render remaining nodes as Textual widgets via _render_node()

Dispatch: _render_<tag> methods for special widgets (tabbedcontent, datatable, static, tree), _render_default for generic widgets via compile_kwargs (module + class).

Attribute classification at mount: for each node attribute:

  1. Constructor parameter → widget.__init__

  2. CSS property → widget.styles

  3. Reactive attribute → widget.set_reactive

Store binding: when a widget has a store attribute (a Bag), _mount subscribes to the Bag for reactive updates. The Tree widget repopulates from the Bag on changes, preserving expanded state.

textual_app.py

TextualApp(BagAppBase) — the puppeteer.

  • page property exposes source Bag (domain name for Textual)

  • recipe(page) — user override

  • render(compiled_bag) — mounts widgets via compiler.render()

  • _on_node_updated(node) — reactive: updates specific widget. Uses call_from_thread only when called from a different thread (remote REPL, timer).

  • _on_widget_changed(widget, value) — bidirectional: widget → data

  • _find_compiled_path(node) — uses Bag.relative_path() to find the node path in the compiled Bag

  • _find_data_path(compiled_path) — reverse-lookup in subscription map

  • run() — creates LiveApp and starts Textual event loop

LiveApp(App) — the puppet.

  • compose() → root Vertical container

  • on_mount() → owner.setup() (recipe + compile + bind + render)

  • Events delegated to owner: button_pressed, key, descendant_blur, input_changed, checkbox_changed, switch_changed

Data Binding

Data to Widget (^pointer)

page.static("^greeting")              # value bound to data["greeting"]
page.input(value="^form.name")        # attr bound to data["form.name"]
page.vertical(width="^_system.w")     # CSS property bound to data path

Flow: data["greeting"] = "Hello" → BindingManager → node updated → _on_node_updated → widget updated.

Widget to Data (bidirectional)

  • Input: writes on blur (via on_descendant_blur), not every keystroke

  • Checkbox/Switch: writes on change (immediate)

Flow: user edits Input → Tab → on_descendant_blur → _on_widget_changed → data.set_item(path, value, _reason=compiled_path) → BindingManager notifies all subscribers except the originator.

Anti-Loop via _reason

When a widget writes to data, it passes its compiled path as _reason. The BindingManager skips updating the node whose path matches the reason. Other widgets bound to the same data path update normally.

Store (Bag-driven Widgets)

The store attribute on a widget receives a Bag object. At mount time:

  1. The Bag reference is saved on the widget (widget._store)

  2. A subscription is registered on the Bag

  3. When the Bag changes, the widget repopulates (e.g., Tree clears and rebuilds, preserving expanded state)

page.tree(label="data", store=self.data)

System Data

Use _system prefix for infrastructure data (drawer state, inspector config) to separate from application data:

self.data["_system.drawer.width"] = 40
self.data["_system.drawer.display"] = "block"

Extending the Builder

Use mixins to add custom elements:

class MyMixin:
    @component(sub_tags="")
    def login_form(self, comp, **kwargs):
        comp.input(placeholder="Username")
        comp.button("Login")

class MyBuilder(MyMixin, TextualBuilder):
    pass

class MyApp(TextualApp):
    builder_class = MyBuilder

The mixin pattern works because _pop_decorated_methods collects decorators from non-BagBuilderBase bases in the MRO.