Asyncio support

The asyncio module built into Python 3.4 and later can be used to write asynchronous code in a single thread. This library supports receiving messages asynchronously in an event loop using the can.Notifier class.

There will still be one thread per CAN bus but the user application will execute entirely in the event loop, allowing simpler concurrency without worrying about threading issues. Interfaces that have a valid file descriptor will however be supported natively without a thread.

You can also use the can.AsyncBufferedReader listener if you prefer to write coroutine based code instead of using callbacks.

Example

Here is an example using both callback and coroutine based code:

#!/usr/bin/env python

"""
This example demonstrates how to use async IO with python-can.
"""

import asyncio
from typing import TYPE_CHECKING

import can

if TYPE_CHECKING:
    from can.notifier import MessageRecipient


def print_message(msg: can.Message) -> None:
    """Regular callback function. Can also be a coroutine."""
    print(msg)


async def main() -> None:
    """The main function that runs in the loop."""

    with can.Bus(
        interface="virtual", channel="my_channel_0", receive_own_messages=True
    ) as bus:
        reader = can.AsyncBufferedReader()
        logger = can.Logger("logfile.asc")

        listeners: list[MessageRecipient] = [
            print_message,  # Callback function
            reader,  # AsyncBufferedReader() listener
            logger,  # Regular Listener object
        ]
        # Create Notifier with an explicit loop to use for scheduling of callbacks
        with can.Notifier(bus, listeners, loop=asyncio.get_running_loop()):
            # Start sending first message
            bus.send(can.Message(arbitration_id=0))

            print("Bouncing 10 messages...")
            for _ in range(10):
                # Wait for next message from AsyncBufferedReader
                msg = await reader.get_message()
                # Delay response
                await asyncio.sleep(0.5)
                msg.arbitration_id += 1
                bus.send(msg)

            # Wait for last message to arrive
            await reader.get_message()
            print("Done!")


if __name__ == "__main__":
    asyncio.run(main())