Some experimentation with combining nicegui (https://nicegui.io/), a Python web frontend with the javascript webserial API. UI elements defined in nicegui are hooked to javascript functions that access the webserial API.
This example interfaces with a PyBadge board (https://learn.adafruit.com/adafruit-pybadge/overview). Light sensor readings are made at a rate of 5 Hz (adjustable) and read from the serial port, triggering a custom asyncrhonous event, and updating the live plot. The NeoPixel LEDs at the bottom of the board can be toggled on or off, demonstrating writing data to the serial port.
main.py -> Python nicegui code. This is the file to run.
script.js -> JavaScript code lives here.
sketch.ino -> Wiring sketch (C code with Adafruit libraries) for target MCU.
Great, you wrote/read to a serial port and threw a web UI on top, big deal. Well...normally, the external hardware would be accessible only through locally-running code. For example, you might have a bunch of clients connecting to a remote server, controlling a remote webcam. In this arrangement the server has a local (physical) connection to the webcam, permitting Python to access it. With webserial, we can invert this relationship. Webserial allows for in-browser access of the local (client) machine's usb/serial ports. This enables the Python backend (running on the remove server) to break throgh the frontend and tunnel out of the browser to the clients' serial port(s). This has a bunch of neat implications for production automation and deployment. For example, we could have local equipment (e.g., test equipment) whose control interface is a web app (instead of a traditionl desktop app or script). Here, there is no need to deploy any local code beyond that of a modern updated browser. Duplicating test stations requires no local Python installation. Code updates can be singularly pushed to the server - no need to update all the clients.