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About

This is an example of how to combine Flet and FastAPI for complex applications which require both an API and a user interface. In this architecture, the API and the user interface are defined in a single app, while being clearly separated. As a result, the back end and the front end can be implemented and published all in one.

When using FastAPI to publish Flet Apps, the Python code is running on the server side and the browser is only displaying it. As a result, the Flet app can access the API internally as a function and doesn't need HTTP requests to communicate with the server.

The Code

Accessing to API functions from the Flet GUI

Each function used by the API can be registered using the @api.register decorator

@api.register
@app.get(f'{path}/set-value')
async def set_value(value: int):
    global counter
    counter = value
    return {'message': f'Updated counter value to {value}'}

api.get() will then produce a dictionary of functions which is passed over to the Flet GUI when creating it.

The Flet app can then save the API functions dictionary as an attribute and make a call to the API whenever needed.

await self.api['set_value'](30)

This is equivalent to https://example.com/flet-fastapi-example/set-value?value=30

Serving a Flet App from FastAPI

@asynccontextmanager
async def lifespan(app: FastAPI):
    await flet_fastapi.app_manager.start()
    yield
    await flet_fastapi.app_manager.shutdown()


async def main(page: ft.Page):
    await gui.init(page, cfg, api.get())

app.mount(f'{path}/', flet_fastapi.app(main))

Idle functions

The code also shows how to create idle functions both in the API (main.py) and in the Flet App (gui.py)

Please note the difference:

  • There is only one API idle function running, because there is only one instance of the API
  • Each Flet App instance (opened Flet Application) has its own idle function

Development

The following files are required:

  • main.py: containing the FastAPI app

  • requirements.txt

  • dockup.yml

    • example

      name: flet-fastapi-example
path: /flet-fastapi-example
type: flet_abs

    • name must match the parent folder name

    • path is the url at which the app will be available.

    • type: must be flet_abs for this type of application

Testing and Deployment

Launch the app in development mode

cd src/flet-fastapi-example
uvicorn main:app --reload --port 8004

The app will be available at localhost:8004/flet-fastapi-example/.

The app will reload itself automatically every time you save the code.

Publish the app using Dockup

About Dockup

Dockup is a CLI tool and Python module which allows to effortlessly publish applications as Docker container.

Please note that you must first install Dockup and a reverse proxy before publishing your app.

Check https://github.com/flokapi/dockup for the installation

Publish locally

Locally

cd src
tar -czf flet-fastapi-example.tar.gz flet-fastapi-example
python3 -m dockup install flet-fastapi-example.tar.gz

The app will be available at http://localhost/flet-fastapi-example/

Publish on your server

Locally

cd src
tar -czf flet-fastapi-example.tar.gz flet-fastapi-example

On your server, once the the archive has been copied

python3 -m dockup install flet-fastapi-example.tar.gz

The app will be available at https://example.com/flet-fastapi-example/

Resources

Flet documentation

Dockup