auserial 0.4.0

Truly async serial port for Linux/macOS using epoll/kqueue

🟧 AUSerial

Truly async serial port for Linux/macOS using epoll/kqueue

Why AUSerial?

AUSerial (Async Unix Serial) is a minimal, dependency-free async serial port for asyncio applications. It relies only on the standard library (os, termios, asyncio) and plugs directly into the event loop via add_reader / add_writer — which under the hood use epoll (Linux) or kqueue (macOS).

Comparison to existing librairies

Library	Backend	Cost
pyserial	Blocking reads	Freezes the event loop
aioserial	run_in_executor around pyserial	One thread per I/O operation
pyserial-asyncio	Transport/Protocol callback API	Verbose, subclass boilerplate
AUSerial	Direct add_reader / add_writer	Zero threads, zero polling

Features

• 🪶 ~80 lines, no external dependencies — just the standard library
• ⚡ Truly non-blocking — no thread pool, no busy loop
• 🔒 Concurrency-safe — internal locks prevent concurrent read/write conflicts
• 🧹 Clean resource management — async context manager + idempotent close()
• 🧯 Proper error propagation through Futures (no silent failures)
• 🧵 Pending operations are cancelled cleanly on close

Installation

pip install auserial

Or from source:

git clone https://github.com/papyDoctor/auserial.git
cd auserial
pip install -e .

Quick Start

import asyncio
from auserial import AUSerial

async def main():
    async with AUSerial("/dev/ttyUSB0") as serial:
        await serial.write(b"AT\r\n")
        data = await serial.read()
        print(f"Received: {data!r}")

asyncio.run(main())

Custom baudrate

import termios
from auserial import AUSerial

async with AUSerial("/dev/ttyUSB0", baudrate=termios.B9600) as serial:
    ...

Timeout

import asyncio

from auserial import AUSerial


async def main():
    async with AUSerial("/dev/cu.usbmodem21301") as serial:
        await serial.write(b"AT\r\n")
        try:
            data = await asyncio.wait_for(serial.read(), timeout=1.0)
        except TimeoutError:
            print("No response within 1s")
        else:
            print(f"Received: {data!r}")


asyncio.run(main())

Discovering ports

from auserial import list_ports

for p in list_ports():
    print(p.path, p.description, p.hwid)
# /dev/cu.usbmodem21301  Raspberry Pi Pico  USB VID:PID=2E8A:0008 SER=E660B4400765AB25

list_ports() is synchronous and returns list[PortInfo]. On Linux it reads USB metadata from /sys/class/tty/<name>/device/. On macOS it parses ioreg output and links each /dev/cu.* to its USB ancestor (Bluetooth and debug consoles are filtered out). Pure stdlib, no extra dependency.

API

Method / function	Description
AUSerial(path, baudrate=...)	Opens the tty in non-blocking mode
await serial.open()	Binds the instance to the current event loop
await serial.read(n_bytes=64)	Waits until data is available, returns bytes
await serial.read_until(terminator=b"\n")	Reads until the terminator is found, returns bytes
await serial.write(data)	Waits until writable, returns bytes written
serial.close()	Cancels pending I/O and closes the fd
list_ports() -> list[PortInfo]	Enumerate available serial ports (sync)
PortInfo(path, description, hwid)	NamedTuple returned by list_ports()

The AUSerial class also implements __aenter__ / __aexit__, so async with is the recommended usage pattern.

Limitations

• Unix-only. Relies on termios and add_reader, which require an epoll/kqueue-compatible file descriptor. Windows needs a different implementation (IOCP).
• A single call to write() issues one os.write — short writes are returned as-is (caller retries with the remainder if needed).

Examples

More usage patterns live in examples/.

License

MIT