How to write a Python async serial async reader?

Question

I am porting some C++ code to Python and I am having a heck of a time figuring out how to have an onReceive handler for serial bytes. I am using

import serial_asyncio
class Arduino: #comms is with an Arduino in serial mode)
    async def connect(self, serial_port):
        (self.serial_reader, self.serial_writer) = await 
        serial_asyncio.open_serial_connection(url=serial_port, baudrate=115200)
        print("serial opened:", serial_port)
        self.buffer = b""

    async def recv(self, data):
        self.buffer += data
        self.process_buffer(self.buffer)

if __name__ == '__main__':
     ardunio = Arduino("/dev/ttyS0")         
     loop = asyncio.get_event_loop()
     loop.run_until_complete(ardunio.connect())
     loop.run_forever()

However I cannot figure out how to patch the recv handler in to the read. I Qt, I could:

connect(&QAbstractSocket::readyRead, &Arduino::handleBytes);

In Node:

arduino.on('data', line => console.log(line))

In Python, there doesn't seem to be any obvious answer? How do I get the serial port bytes that arrive to be passed into Arduino.receive(self, data)?