nats-io/nats.py nats-core/v0.1.0

on GitHub

Initial release of nats-core, a lean and fast Python client for the NATS messaging system.

Features

• Publish/Subscribe - Core pub/sub messaging with wildcard subscriptions
• Request/Reply - Synchronous request-response pattern with timeout support
• Queue Groups - Load balancing across subscribers
• Message Headers - Multi-value header support (NATS 2.2+)
• Automatic Reconnection - Configurable reconnect with backoff and jitter
• TLS Support - Secure connections with custom SSL contexts
• Authentication - Token, username/password, NKey, and JWT/credentials file support
• Async Context Manager - Clean resource management with async with
• Connection Statistics - Track messages/bytes sent and received
• Slow Consumer Detection - Configurable pending limits with callbacks

Requirements

• Python 3.13+
• No required dependencies (optional nkeys for NKey authentication)

Installation

# For now, this is standalone outside of the nats-py package.
pip install nats-core

Quick Start

import asyncio

from nats.client import connect

async def main():
    async with await connect("nats://localhost:4222") as client:
        sub = await client.subscribe("greet")
        await client.publish("greet", b"Hello, NATS!")
        msg = await sub.next()
        print(f"Received: {msg.data.decode()}")

asyncio.run(main())

Performance

Performance is substantially improved compared to nats-py.

Benchmarks on Apple M3 Max (1M messages, publisher and subscriber in same process):

Queue Mode (subscriber throughput):

* nats-py dropped 47-87% of messages under load

Zero message loss with nats-core across all configurations.