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pgwidgets — Python Bindings

Python bindings for the pgwidgets JavaScript widget library. Build desktop-style browser UIs from Python with a familiar Qt/GTK-style API.

Documentation

Full documentation is available at pgwidgets-python.readthedocs.io.

Installation

pip install pgwidgets-python

This will also install pgwidgets-js (the JavaScript assets) and websockets as dependencies.

Quick Start

from pgwidgets.sync import Application

app = Application()

@app.on_connect
def setup(session):
    Widgets = session.get_widgets()

    top = Widgets.TopLevel(title="Hello", resizable=True)
    top.resize(400, 300)

    vbox = Widgets.VBox(spacing=8, padding=10)
    btn = Widgets.Button("Click me")
    label = Widgets.Label("Ready")

    btn.on("activated", lambda: label.set_text("Clicked!"))

    vbox.add_widget(btn, 0)
    vbox.add_widget(label, 1)
    top.set_widget(vbox)
    top.show()

app.run()

Run the script, then open the printed URL in your browser.

Sync vs Async

Both APIs provide the same widget classes and methods.

Synchronous (recommended for most use cases):

from pgwidgets.sync import Application
app = Application()

@app.on_connect
def setup(session):
    Widgets = session.get_widgets()
    btn = Widgets.Button("Click")      # blocking call
    btn.set_text("New text")           # blocking call

app.run()

Asynchronous (for asyncio applications):

from pgwidgets.async_ import Application
app = Application()

@app.on_connect
async def setup(session):
    Widgets = session.get_widgets()
    btn = await Widgets.Button("Click")    # awaitable
    await btn.set_text("New text")         # awaitable

await app.run()

How It Works

The Application class starts two servers:

  • An HTTP server (default port 9501) that serves the pgwidgets JS/CSS and a connector page
  • A WebSocket server (default port 9500) for the JSON command protocol

When you open the URL in a browser, the page loads pgwidgets and connects back over WebSocket. Python widget constructors and method calls are translated to JSON messages and executed in the browser. Callbacks are forwarded back to Python.

Sessions and Reconnection

Sessions persist independently of browser connections. When a browser disconnects (page refresh, network drop, tab close), the session and its widget tree remain alive on the Python side. When the browser reconnects, the entire UI is automatically reconstructed.

app = Application(max_sessions=4, logger=logger)

@app.on_connect
def setup(session):
    Widgets = session.get_widgets()
    # Build your UI...
    # If the browser refreshes, this UI is reconstructed automatically.

Key features:

  • Automatic reconstruction -- refresh the browser and the UI reappears in its current state (widget positions, text, slider values, etc.).
  • Multi-browser support -- open the same session URL in a second browser tab or window. Both browsers show the same UI and stay synchronized. Widget state changes (slider moves, tab switches, tree expand/collapse) are pushed to all connected browsers in real time.
  • Headless sessions -- create sessions without a browser using app.create_session(), build the widget tree, then connect a browser later to see the pre-built UI.

License

BSD 3-Clause