novabus

A dependency-free, in-process, priority-aware event bus for Python asyncio apps.

No PyQt5, no Redis, no broker to run. Pure stdlib (asyncio + collections).

pip install -e .   # from this directory, until it's published

Usage

import asyncio
from novabus import Bus

loop = asyncio.get_event_loop()
bus = Bus(loop=loop)

# mark which (source, function_name) pairs jump the queue
bus.mark_critical("TradingSignal", "interpret_trading_signal")

def on_event(source, function_name, result, params):
    print(source, function_name, result, params)

bus.subscribe("my_module", on_event, sources=["TradingSignal"])  # or sources=None for all
bus.start()

bus.publish("TradingSignal", "interpret_trading_signal", result={"side": "buy"}, params={})

For maximum throughput when ordering/priority don't matter, call bus.set_high_rate_mode(True) — publish then dispatches synchronously, bypassing the queue.

Design notes

• Two priority lanes (critical / non-critical); critical always drains first and pauses non-critical delivery until caught up.
• Per-event dedup via a monotonic counter (bounded memory, periodically evicted).
• Stale-event flushing: events older than stale_after seconds are dropped instead of being delivered late.
• Backpressure: queue has a max size; oldest non-critical events are dropped first when full.
• Subscribers are plain callables, optionally filtered by source/function name.

Benchmark

python bench.py publishes 200k events and measures end-to-end delivery. On a typical dev machine: ~245k events/sec in normal (priority-queue) mode, ~800k events/sec in high_rate_mode.