Registered Event Listener (rel)

0.4.9.26 verified Mon Apr 27 auth: no python

Rel is a lightweight (0.4.9.26) event/observer pattern library for Python that implements the standard pyevent interface without external dependencies. It provides a simple publish-subscribe mechanism with event registration, firing, and listener management. The library is API-stable with infrequent releases.

pip install rel

Common errors

error AttributeError: module 'rel' has no attribute 'event' ↓

cause Attempting to import from rel.event which does not exist as a submodule.

fix

Use: from rel import EventHandler (or simply import rel and use rel.add/fire).

error NameError: name 'add' is not defined ↓

cause Importing incorrectly: from rel import * does not export add due to __all__ not defined.

fix

Use: from rel import add (or import rel and then rel.add).

Warnings

gotcha The library is single-threaded by default. Do not assume thread safety; use rel's own async/schedule features for concurrent patterns. ↓

fix Use rel.timeout or rel.schedule for timed callbacks, not threading.Thread.

gotcha EventHandler is deprecated; use the module-level functions (add, fire, remove) instead. ↓

fix Replace EventHandler instances with rel.add() and rel.fire(). Visit documentation for migration.

gotcha When using rel.fire_in() or rel.schedule(), the program will exit immediately unless rel.dispatch() is running. These methods schedule on an internal timer that only fires while dispatch() is active. ↓

fix Call rel.dispatch() (blocking) to start the event loop after scheduling. Use a non-blocking alternative like rel.timeout if you need async in a GUI framework.

Imports

rel
```
import rel
```
Direct import of the package.
EventHandler
wrong
```
from rel.event import EventHandler
```
correct
```
from rel import EventHandler
```
EventHandler is a top-level module, not a sub-package.
add
```
from rel import add
```
add is a top-level function to register listeners.
fire
```
from rel import fire
```
fire is a top-level function to trigger events.

Quickstart

Basic usage: add listeners, fire events synchronously or with a delay.

import rel

# Register an event listener
def my_handler(data):
    print(f"Received: {data}")

rel.add('my_event', my_handler)

# Fire an event
rel.fire('my_event', {'key': 'value'})

# Remove listener
rel.remove('my_event', my_handler)

# Fire event after 1 second
rel.fire_in(1.0, 'my_event', 'hello')