zuvloop¶

A libuv event loop for asyncio, written in Zig.

Source Code: https://github.com/Kludex/zuvloop

zuvloop replaces the asyncio event loop with one whose hot paths are implemented natively and driven by libuv. It is a drop-in replacement: you hand it to asyncio.run() and everything you already wrote keeps working.

It is the same idea as uvloop, with a Zig core instead of Cython, type hints that pass a strict type checker, and OpenTelemetry instrumentation built in.

The key features are:

• Fast: faster than uvloop on every benchmark in the suite. See Performance.
• Drop-in: a loop factory. No API of its own to learn, no framework to adopt.
• Typed: a strict-mypy-clean Python surface, shipped with a py.typed marker.
• Observable: plain OpenTelemetry spans, counters and gauges, measured in Zig. No vendor SDK, and nothing to pay when nobody is listening.

Installation¶

$ pip install zuvloop

Example¶

import asyncio

import zuvloop


async def main() -> None:
    reader, writer = await asyncio.open_connection("example.com", 80)
    writer.write(b"GET / HTTP/1.0\r\nHost: example.com\r\n\r\n")
    await writer.drain()
    print(await reader.read(64))
    writer.close()
    await writer.wait_closed()


zuvloop.run(main())

zuvloop.run() is asyncio.run() with the loop swapped. You can also hand the factory to asyncio yourself:

asyncio.run(main(), loop_factory=zuvloop.new_event_loop)

Nothing else in your program changes. That is the whole integration surface, and Running the loop covers the rest of it.

Why a new loop¶

uvloop has been the answer for a decade, and it is a good one. zuvloop differs in three ways that matter if you are choosing between them.

It is faster. Not by a lot everywhere, but by a lot in the places where a loop can be. Writes issued during one turn go out as a single vectored syscall, which is worth 20% on a real ASGI server because a response is sent as a header write and a body write. Address literals never reach getaddrinfo.

It agrees with asyncio. Its transports are real asyncio.Transport subclasses, loop.time() is time.monotonic(), and get_extra_info("socket") returns a TransportSocket. Those sound like details until a library asserts on one. Compatibility records where zuvloop and uvloop each diverge from the standard library, with the cases measured rather than claimed.

It is typed and instrumented. The Python surface passes mypy --strict, and the loop emits OpenTelemetry without you importing an SDK.

Requirements¶

Python 3.14+, on Linux or macOS.