https://github.com/florimondmanca/arel
Lightweight browser hot reload for Python ASGI web apps
https://github.com/florimondmanca/arel
asgi browser fastapi hot-reload python starlette websockets
Last synced: 16 days ago
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Lightweight browser hot reload for Python ASGI web apps
- Host: GitHub
- URL: https://github.com/florimondmanca/arel
- Owner: florimondmanca
- License: mit
- Created: 2020-04-03T20:39:06.000Z (about 5 years ago)
- Default Branch: master
- Last Pushed: 2024-04-26T12:41:50.000Z (12 months ago)
- Last Synced: 2025-03-29T14:06:34.864Z (23 days ago)
- Topics: asgi, browser, fastapi, hot-reload, python, starlette, websockets
- Language: Python
- Homepage: https://pypi.org/project/arel
- Size: 72.3 KB
- Stars: 151
- Watchers: 4
- Forks: 6
- Open Issues: 6
-
Metadata Files:
- Readme: README.md
- Changelog: CHANGELOG.md
- License: LICENSE
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README
# arel
[](https://dev.azure.com/florimondmanca/public/_build/latest?definitionId=6&branchName=master)
[](https://codecov.io/gh/florimondmanca/arel)
[](https://pypi.org/project/arel)
Browser hot reload for Python ASGI web apps.
## Overview
**What is this for?**
`arel` can be used to implement development-only hot-reload for non-Python files that are not read from disk on each request. This may include HTML templates, GraphQL schemas, cached rendered Markdown content, etc.
**How does it work?**
`arel` watches changes over a set of files. When a file changes, `arel` notifies the browser (using WebSocket), and an injected client script triggers a page reload. You can register your own reload hooks for any extra server-side operations, such as reloading cached content or re-initializing other server-side resources.
## Installation
```bash
pip install 'arel==0.3.*'
```
## Quickstart
_For a working example using Starlette, see the [Example](#example) section._
Although the exact instructions to set up hot reload with `arel` depend on the specifics of your ASGI framework, there are three general steps to follow:
1. Create an `HotReload` instance, passing one or more directories of files to watch, and optionally a list of callbacks to call before a reload is triggered:
```python
import arel
async def reload_data():
print("Reloading server data...")
hotreload = arel.HotReload(
paths=[
arel.Path("./server/data", on_reload=[reload_data]),
arel.Path("./server/static"),
],
)
```
2. Mount the hot reload endpoint, and register its startup and shutdown event handlers. If using Starlette, this can be done like this:
```python
from starlette.applications import Starlette
from starlette.routing import WebSocketRoute
app = Starlette(
routes=[WebSocketRoute("/hot-reload", hotreload, name="hot-reload")],
on_startup=[hotreload.startup],
on_shutdown=[hotreload.shutdown],
)
```
3. Add the JavaScript code to your website HTML. If using [Starlette with Jinja templates](https://www.starlette.io/templates/), you can do this by updating the global environment, then injecting the script into your base template:
```python
templates.env.globals["DEBUG"] = os.getenv("DEBUG") # Development flag.
templates.env.globals["hotreload"] = hotreload
```
```jinja
{% if DEBUG %}
{{ hotreload.script(url_for('hot-reload')) | safe }}
{% endif %}
```
## Example
The [`example` directory](https://github.com/florimondmanca/arel/tree/master/example) contains an example Markdown-powered website that uses `arel` to refresh the browser when Markdown content or HTML templates change.
## License
MIT