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tempestweb

📚 Documentation: Português (Brasil) · English (US) — bilingual docs site (PT-BR default + EN-US), deployed to GitHub Pages.

Build web apps in typed Python. One declarative widget tree, a DOM renderer, and three execution modes that share 100% of the application code: Mode A (WASM) runs your Python in the browser via Pyodide; Mode B (server) runs it on the server (FastAPI) and talks to a thin JS client over WebSocket or SSE; Mode C (transpile, experimental) transcribes your Python to native JavaScript — zero Python runtime, static hosting, great first-paint/SEO. Installable PWA, offline-first (service worker + IndexedDB), and WebPush are first-class — parity with tempest-react-sdk.

Sister project to tempestroid — same "one tree, multiple renderers" architecture. The renderer-agnostic engine (IR, reconciler, state, style, widgets) is shared; tempestweb adds a DOM leaf renderer (pure JavaScript, no framework, no build step, no TypeScript) and two patch transports.

Status

🚧 Early construction. See the design docs:

Want runnable apps? Browse the Example Gallery (PT-BR) — 41 single-concept demos (stopwatch, forms, data table/grid, kanban, chat, theming, i18n, canvas charts, app shells, native capabilities, observability, PWA/WebPush, and a server-mode walkthrough), each running unchanged in both modes.

Building something real? Read the App architecture & best practices guide (EN) — the ideal layered structure (routes · pages · components · styles · controllers · services · storages · schemas · utils · core), mirroring tempest-fastapi-sdk, so your app doesn't rot into garbage code.

How it works

   view(app) ──build──▶ Node tree (IR)        ← shared core (vendored from tempestroid)
                            │
                          diff
                            ▼
                        [ Patch ]              insert / remove / update / reorder / replace
                       ╱          ╲
              Mode A transport   Mode B transport
              (pyodide.ffi)       (WebSocket | SSE)
                       ╲          ╱
                  client/ (pure JS): apply patches to the DOM
                  + Style→CSS + event capture                  ← same code in both modes

The application's view() never names a transport — the same examples/counter/app.py runs under --mode wasm and --mode server unchanged. Capabilities (native/: http, audio, share, geolocation, clipboard, storage, camera) are typed awaitables with the same Python API in both modes — Mode A calls the Web API in-process, Mode B proxies it over a round-trip (see docs/contract.md).

Static SSR — render_to_html

A third render target, alongside the two interactive modes: the same typed tree renders to a static HTML string on the server — no JavaScript, no DOM, no runtime. HTML is just another leaf renderer.

from tempest_core import Column, Text, Button, Style
from tempest_core.style import Edge
from tempestweb.html import render_to_html, render_document

tree: Column = Column(
    style=Style(gap=8.0, padding=Edge.all(16)),
    children=[Text(content="Hello"), Button(label="Click")],
)

fragment: str = render_to_html(tree)                 # an HTML fragment
page: str = render_document(tree, title="Home", htmx=True)  # a full document

The CSS is byte-identical to what the DOM client emits (the style_to_css port mirrors client/style.js), and the new tempest-core 0.9.0 Widget.tag / Widget.attrs fields let you emit semantic, htmx-ready markup (Container(tag="nav", attrs={"hx-get": "/x"})). All text/attributes are escaped. See the Static SSR guide (EN).

Mode C — transpile to native JS (experimental) 🧪

The "TypeScript story" for Python: you write the typed-Python app; a compiler transcribes the app layer (state, view(), handlers) to native JavaScript, reusing the whole shared JS renderer. Zero Python runtime in the browser — static hosting, small bundle, great first-paint/SEO.

# examples/counter/app.py  (unchanged from Modes A/B)
@dataclass
class CounterState:
    value: int = 0

def view(app: App[CounterState]) -> Widget:
    def increment() -> None:
        app.set_state(lambda s: setattr(s, "value", s.value + 1))
    return Column(children=[
        Text(content=f"Count: {app.state.value}", key="label"),
        Button(label="+", on_click=increment, key="inc"),
    ])
from tempestweb.transpile import transpile_file

js: str = transpile_file("examples/counter/app.py")  # -> native ES module

The generated module runs on the native runtime (client/transpile/runtime.js) with a JS diff locked against a core-derived golden. Experimental (spike C0): MD3 style fidelity, a build --mode transpile CLI, and a wider subset are next (phases C1–C5). See docs/modo-c-transpile.md.

Develop

uv venv && uv pip install -e ".[dev,server,cli]"
make check          # ruff + mypy + pytest + JS (jsdom) tests

Layout

Path What
tempest-core (dependency) Renderer-agnostic engine — IR/reconciler/state/style/widgets (import tempest_core), extracted from tempestroid.
tempestweb/components/ Native fields + forms (EmailField, PasswordField, LoginForm, …) plus the re-exported tempest-core library — 54 Material 3 components (Card, DataTable, Tabs, Drawer, Alert, BarChart/LineChart, …).
tempestweb/transports/ The one seam between modes (base.py Protocol, wasm.py, websocket.py, sse.py).
tempestweb/html/ Static SSR leaf renderer — render_to_html / render_document / style_to_css (Python port of client/style.js).
tempestweb/transpile/ Mode C (experimental): ast-based Python→JS compiler for the app layer. Paired with the native runtime in client/transpile/ (diff.js · widgets.js · runtime.js).
tempestweb/server/ FastAPI + WebSocket/SSE host (Mode B).
tempestweb/native/ Web API capability adapters — http, audio, share, geo, clipboard, storage, camera (Track N).
tempestweb/observability/ Telemetry, logger, error boundary, feature flags, auth — adapter pattern (Track O).
tempestweb/pwa/ Web App Manifest + icon emitter (Track P).
tempestweb/cli/ tempestweb new/dev/build/run/sync.
client/ Pure-JS DOM renderer (incl. Canvas draw-command execution for charts), Style→CSS, event capture; pwa/ sw/ offline/ push/ native/ subdirs.
tests/fixtures/ Golden wire-format fixtures derived from the core.

Conventions

Python: double quotes, full typing (mypy --strict), Google docstrings in English, async-first. Client: plain JavaScript only — no TypeScript, no framework, no build step. See CLAUDE.md.

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