events

library0.5pypypi✓ verified 29d ago

The 'events' library for Python, currently at version 0.5, aims to bring the elegance of C# EventHandler to Python. It provides a simple, lightweight mechanism for event subscription and firing, encapsulating the core functionality for attaching and invoking callback functions (event handlers) in sequence, thus facilitating event-driven programming patterns in a straightforward manner. The library is considered mature and stable, with its last release in July 2023, and sees infrequent updates.

communication

pip install events

github ↗package ↗

INSTALL

IMPORT

SIG · EVENTS

events

communicationpythonv0.5

Install

1.6s avg

Import

—

Disk

16MB

Pass rate

10/ 10

Env Coverage10 / 10

glibc

3.9–3.13

musl

3.9–3.13

Install & Compatibility

Where this runs

tested against v0.5 · pip install

no network on importno background threads

Install × environment matrix

Each cell = how many times install + import succeeded across repeated harness runs. Partial = flaky.
glibc = Debian/Ubuntu slim · musl = Alpine Linux

musl

py 3.10–3.95 runs

installs and imports cleanly · install 0.0s · import 0.000s · 17.8MB

glibc

py 3.10–3.95 runs

installs and imports cleanly · install 1.6s · import 0.000s · 18MB

16MB installed

● package 16MB

Code

Verified usage

Verified import paths — ran on the pinned version, not inferred.

Events

✓ from events import Events

The primary class for creating event publishers.

Demonstrates how to create an `Events` object, subscribe multiple callback functions using `+=`, fire events, and unsubscribe callbacks using `-=`.

from events import Events def my_event_handler(reason, data=None): print(f"Event fired: {reason}") if data: print(f" Data: {data}") # Create an Events instance app_events = Events() # Subscribe a handler to an event named 'on_change' app_events.on_change += my_event_handler # Fire the 'on_change' event print("Firing event: 'initial change'") app_events.on_change("initial change", data={"user": "admin"}) # Subscribe another handler to the same event def another_handler(reason): print(f"Another handler received: {reason}") app_events.on_change += another_handler # Fire the event again print("\nFiring event again: 'second change'") app_events.on_change("second change") # Unsubscribe a handler app_events.on_change -= my_event_handler # Fire the event one last time (only 'another_handler' will be invoked) print("\nFiring event after unsubscription: 'final change'") app_events.on_change("final change")

Debug

Known issues

gotchaThe `Events()` instance holds strong references to subscribed callback functions. If an event handler is a method of an object, and the `Events` instance outlives that object, it can prevent the object from being garbage collected, leading to memory leaks. Always explicitly unsubscribe handlers using `-=` when they are no longer needed, especially for object methods.

fix

Ensure `event_instance.event_name -= handler_function` is called when the handler is no longer required or the associated object is being disposed of. Consider weak references for advanced scenarios if manual unsubscription is problematic.

affects: 0.1 - 0.5

gotchaBy default, `Events` instances do not predefine event names. This means you can subscribe to and fire any arbitrary event name (e.g., `events.on_typo`). This flexibility can lead to subtle bugs due to typos in event names that might go unnoticed. For stricter validation, you can predefine events.

fix

To enforce predefined events, subclass `Events` and list event names in the class definition, or pass an iterator of event names to the `Events` constructor. Attempts to subscribe to or fire an undefined event will then raise an `EventsException`.

affects: 0.1 - 0.5

gotchaThe package name 'events' is highly generic. There are several other Python libraries and standard library modules (e.g., `eventsourcing`, `pyventus`, `python-dispatch`, `threading.Event`) that deal with event-related patterns. Ensure you are installing and using `pyeve/events` if this is your intended library.

fix

Always import explicitly (e.g., `from events import Events`) and check the `events.__file__` to confirm you're using the correct package. Refer to documentation specific to `github.com/pyeve/events`.

affects: All versions

Errors

Common errors & fixes

ModuleNotFoundError: No module named 'events'

The 'events' package has not been installed in your Python environment or there is a typo in the import statement.

fix

Install the library using pip: `pip install Events`. Ensure your import statement is `from events import Event`.

AttributeError: 'Event' object has no attribute '...' (e.g., 'name', 'type')

The base `events.Event` object does not automatically possess arbitrary attributes like 'name' or 'type'. Event data is typically accessed via `event.sender`, `event.args` (for positional arguments), or `event.kwargs` (for keyword arguments).

fix

Access event data using `event.sender`, `event.args`, or `event.kwargs`. If you intend to pass named data, use keyword arguments when firing the event and access them via `event.kwargs['your_key']`.

TypeError: handler_function() missing X required positional argument: 'Y'

An event handler function was subscribed with a signature (parameters) that does not match the arguments provided when the event is fired.

fix

Ensure that the event handler function's parameters (`sender`, `*args`, `**kwargs`) correctly correspond to the arguments passed to `event.fire(sender, *args, **kwargs)`.

Upgrade

Version history

0.5latest on PyPI · released Jul 31, 2023

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Dependencies

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Agent activity

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Resources

githubhttp://github.com/pyeve/events ↗

packagehttps://pypi.org/project/events/ ↗