Flet for Python

0.84.0 · active · verified Wed Apr 15

Flet is a Python library for easily building interactive multi-platform apps using Flutter under the hood. It allows developers to create beautiful desktop, web, and mobile applications with pure Python, leveraging a declarative UI framework. Currently at version 0.84.0, Flet maintains a rapid release cadence, often with weekly development builds and bi-weekly stable releases.

Warnings

gotcha After modifying any control's properties (e.g., `text_control.value = 'new_value'`), you must call `page.update()` (or `control.update()`, `view.update()`) for changes to be reflected in the UI. Forgetting this is a very common beginner mistake.
Fix: Always call `page.update()` or `control.update()` after changing properties of a UI control within an event handler or any function that modifies the page's state.
breaking In version 0.83.1, properties `delta_x` and `delta_y` in certain event objects (e.g., for mouse events) were replaced with `local_delta.x` and `local_delta.y`. Code relying on the old properties will break.
Fix: Update event handlers to use `e.local_delta.x` and `e.local_delta.y` instead of `e.delta_x` and `e.delta_y`.
gotcha Due to rapid development, Flet's API can change frequently, especially for control properties and event signatures. Code written for one minor version might require adjustments for a newer one.
Fix: Always refer to the official Flet documentation for your installed version (`flet --version`) to ensure correct API usage. Pay close attention to changelogs for breaking changes between versions.
gotcha Packaging Flet applications into standalone executables using `flet pack` can sometimes be platform-specific or encounter build issues, particularly on macOS, as noted in recent development releases.
Fix: Ensure `flet-cli` is up-to-date (`pip install flet --upgrade`). If issues persist, consult the Flet GitHub issues, community discussions, or consider alternative packaging tools like PyInstaller with custom Flet hooks if available.

Install

pip install flet Install Flet

Imports

ft
```
import flet as ft
```
app
```
ft.app(target=main)
```
Page
wrong:
```
from flet import Page
```
correct:
```
def main(page: ft.Page):
```
Most Flet components and functions are typically imported via 'import flet as ft' for consistency and easy access.

Quickstart

This quickstart demonstrates a simple counter application. It showcases basic UI components like `Text` and `IconButton`, event handling (`on_click`), and the critical `page.update()` method for refreshing the UI after state changes.

import flet as ft

def main(page: ft.Page):
    page.title = "Flet Counter App"
    page.vertical_alignment = ft.MainAxisAlignment.CENTER

    txt_number = ft.Text("0", size=30)

    def minus_click(e):
        txt_number.value = str(int(txt_number.value) - 1)
        page.update()

    def plus_click(e):
        txt_number.value = str(int(txt_number.value) + 1)
        page.update()

    page.add(
        ft.Row(
            [
                ft.IconButton(ft.icons.REMOVE, on_click=minus_click),
                txt_number,
                ft.IconButton(ft.icons.ADD, on_click=plus_click),
            ],
            alignment=ft.MainAxisAlignment.CENTER,
        )
    )

ft.app(target=main)

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