Prefab

0.19.1 verified Sat May 09 auth: no python

Prefab is a generative UI framework for Python by PrefectHQ. It allows building interactive web UIs with pure Python, using reactive components. Current version: 0.19.1, requires Python >=3.10. Release cadence is active with frequent minor/patch releases.

pip install prefab-ui

Common errors

error ModuleNotFoundError: No module named 'prefab_ui' ↓

cause Importing using the PyPI package name instead of the correct module name.

fix

Replace import prefab_ui with import prefab.

error AttributeError: module 'prefab' has no attribute 'Button' ↓

cause Trying to import a component directly from the top-level prefab module.

fix

Use from prefab.components import Button.

error TypeError: App.__init__() got an unexpected keyword argument 'something' ↓

cause Passing unsupported arguments to App constructor; App only accepts components and basic config.

fix

Check App signature: App(*components, title='', ...).

error ValueError: 'from_model' requires a Pydantic model class ↓

cause Form.from_model() called with an object that is not a Pydantic BaseModel subclass.

fix

Ensure the class inherits from pydantic.BaseModel.

error prefab.exceptions.PrefabRuntimeError: Reactive state not bound to component ↓

cause Using a reactive state variable outside a component's render context.

fix

Access reactive state only within component callbacks or render functions.

Warnings

gotcha Import as `prefab` not `prefab_ui` – the PyPI package name and import name differ. ↓

fix Use `import prefab` or `from prefab import ...`

gotcha Components must be imported from `prefab.components` submodule, not directly from `prefab`. ↓

fix Use `from prefab.components import Button, Form, ...`

gotcha Reactive state management requires understanding `prefab.state` and reactive variables; misuse can cause silent UI failures. ↓

fix Use `prefab.state.State` or `prefab.state.Reactive` for mutable state.

gotcha The `Form.from_model` runtime prefill feature was added in v0.19.1; earlier versions do not support `defaults` kwarg. ↓

fix Upgrade to 0.19.1+ or implement prefill manually.

gotcha Charts default to `show_legend=True` only from v0.17.0+; earlier versions had no legend. ↓

fix Upgrade to 0.17.0+ or set `show_legend=True` explicitly.

Imports

prefab
wrong
```
import prefab_ui
```
correct
```
import prefab
```
The PyPI package name differs from the import name; always import as 'prefab'.

App

wrong

from prefab_ui import App

correct

from prefab import App

Wrong package name in import path.

Button
```
from prefab.components import Button
```
Components are submodules; common mistake is to import from prefab directly.
Form
```
from prefab.components import Form
```
Form.from_model() is used for model-based forms.

Quickstart

Minimal app with a button, served locally.

import prefab
from prefab import App, components

app = App(
    components.Button(text="Hello, World!")
)

if __name__ == "__main__":
    app.serve()