# arel
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Browser hot reload for Python ASGI web apps.
![](https://media.githubusercontent.com/media/florimondmanca/arel/master/docs/demo.gif)
## 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
_This is project in early alpha status. Be sure to pin your dependencies._
```bash
pip install 'arel==0.1.*'
```
## 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
<body>
<!-- Page content... -->
<!-- Hot reload script -->
{% if DEBUG %}
{{ hotreload.script(url_for('hot-reload')) | safe }}
{% endif %}
</body>
```
## 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
# Changelog
All notable changes to this project will be documented in this file.
The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
## 0.2.0 - 2020-07-08
### Added
- Add support for watching multiple directories, each with its own reload callbacks. (Pull #15)
### Changed
- `arel.HotReload("./directory", on_reload=[...])` should now be written as `arel.HotReload(paths=[arel.Path("./directory", on_reload=[...])])`. (Pull #15)
## 0.1.0 - 2020-04-11
_Initial release._
### Added
- Add `HotReload` ASGI application class. (Pull #1)