genro-builders

Builder system for genro-bag — grammar, validation, reactive data binding, and computed data infrastructure.

Installation

pip install genro-builders

Quick start

from genro_builders.contrib.html import HtmlBuilder

builder = HtmlBuilder()
body = builder.source.body()
body.div(id='main').p('Hello, world!')

builder.build()
print(builder.render())

The manager pattern — store() and main()

A builder is a machine. To define what to build, use a BuilderManager:

from genro_builders.contrib.html import HtmlBuilder
from genro_builders.manager import BuilderManager

class HtmlManager(BuilderManager):
    def __init__(self):
        self.page = self.set_builder('page', HtmlBuilder)

    def render(self):
        return self.page.render()

class MyPage(HtmlManager):
    def __init__(self):
        super().__init__()
        self.setup()       # store -> main
        self.build()       # source -> built

    def store(self, data):
        data['title'] = 'Hello, world!'

    def main(self, source):
        body = source.body()
        body.h1(value='^title')
        self.footer(source)

    def footer(self, source):
        source.footer().p('(c) 2026')

page = MyPage()
print(page.render())

Features

• Domain-specific grammars — Define elements, validation rules, and components via decorators (@element, @abstract, @component)
• Data infrastructure — @data_element decorator for data_setter, data_formula, and data_controller — write, compute, and act on the reactive data store directly from the source Bag
• Reactive formulas — data_formula with ^pointer dependencies re-executes automatically when sources change, in topological order (dependencies first, cycles detected)
• Computed attributes — Callable attributes with ^pointer defaults are resolved just-in-time during render/compile
• Debounce and periodic — _delay for debounced formula re-execution, _interval for periodic polling
• Output suspension — suspend_output() / resume_output() to batch data changes and trigger a single render
• Pointer formali — The built Bag retains ^pointer strings; resolution happens just-in-time during render/compile, not during build
• Named slots — Components can declare insertion points (slots=['left', 'right']) for user content injection
• Contributed builders — HTML5, Markdown, SVG, XSD in genro_builders.contrib (optional, not loaded unless imported)
• Multi-builder coordination — BuilderManager coordinates multiple builders with a shared data store
• Renderers and compilers — @renderer for serialized output (HTML, Markdown), @compiler for live objects (widgets, workbooks)
• Node identification — node_id attribute for O(1) lookup via node_by_id()
• Validation — sub_tags cardinality, parent_tags constraints, typed attribute validation via Annotated

Architecture

A builder is a machine that materializes a source Bag into a built Bag. A BuilderManager mixin orchestrates population and lifecycle:

setup()           ->  build()              ->  subscribe()     ->  render() / compile()
store + main          two-pass walk:           activate            output
(populate)            1. data elements         reactivity
                      2. normal elements

• setup() — on manager: calls store(data) then main(source)
• build() — two-pass materialize:
  • Pass 1: process data elements (data_setter writes values, data_formula computes, data_controller executes side effects)
  • Pass 2: materialize normal elements and components into the built Bag, register ^pointer bindings
  • After both passes: topological sort of formulas, fire _onBuilt hooks
• subscribe() — optional: activate reactive bindings. Data changes trigger formula re-execution and automatic re-render. Starts _interval timers.
• render() — produce serialized output via BagRendererBase (just-in-time ^pointer resolution)
• compile() — produce live objects via BagCompilerBase (just-in-time ^pointer resolution)

Data infrastructure

Data elements let you define computed and reactive data directly in the source Bag:

from genro_builders.contrib.html import HtmlBuilder

builder = HtmlBuilder()
s = builder.source

# Static data
s.data_setter('greeting', value='Hello')

# Computed data (re-executes when ^greeting changes)
s.data_formula('message', func=lambda greeting: f'{greeting}, World!',
               greeting='^greeting')

# Controller (side effect, no output path)
s.data_controller(func=lambda message: print(f'Message: {message}'),
                   message='^message')

# UI bound to computed data
s.body().h1(value='^message')

builder.build()
builder.subscribe()
print(builder.output)
# <body><h1>Hello, World!</h1></body>

# Change source data -> formula re-executes -> re-render
builder.data['greeting'] = 'Ciao'
print(builder.output)
# <body><h1>Ciao, World!</h1></body>

Debounce and periodic execution

# Re-execute at most once every 500ms (debounce)
s.data_formula('search_results', func=do_search,
               query='^search.query', _delay=0.5)

# Re-execute every 10 seconds (polling)
s.data_formula('clock', func=lambda: time.strftime('%H:%M:%S'),
               _interval=10.0)

Output suspension

builder.suspend_output()     # pause rendering
builder.data['a'] = 1
builder.data['b'] = 2
builder.data['c'] = 3        # no render triggered yet
builder.resume_output()       # single render with all 3 changes

Documentation

See the docs/ directory for full documentation:

• Getting Started — Build your first page in 5 minutes
• Custom Builders — Define your own grammar
• Reactive Data — Data elements, formulas, reactivity
• Architecture — Build pipeline, pointer formali, formula registry

License

Apache License 2.0 — Copyright 2025 Softwell S.r.l.