Await for function until it receives a callback in python async IO

I have created a GATT Client in python using the Bleak Library. I subscribe to a notification characteristic and after when I get the callback in the notification handler function, I do a write to a characteristic.Until now, after I start the notification I used put a asyncio.sleep for 5 seconds and then I would do a write on the characteristic. But this is very flaky and there is no control over the code, so I want to wait until I receive a callback in notification handler function and when I get the response, I want to do the write. I am new to python async IO and I am not sure how to achieve this. Thanks for your time and effort.

Here is the Code:

import logging
import asyncio
import platform

from bleak import BleakClient
from bleak import _logger as logger
import time

from concurrent.futures import ThreadPoolExecutor

CHARACTERISTIC_UUID = "0000c305-0000-1000-8000-00805f9b34fb"
CHARACTERISTIC_UUID_WR = "0000c303-0000-1000-8000-00805f9b34fb"
CHARACTERISTIC_UUID_RD = "0000c301-0000-1000-8000-00805f9b34fb"

_executor = ThreadPoolExecutor(1)

async def notification_handler(sender, data):
    """Simple notification handler which prints the data received."""
    print("{0}: {1}".format(sender, data))
    print(hexdump(data, 16))


def hexdump(src, length=16):
        result = []
        digits = 4 if isinstance(src, str) else 2
        for i in range(0, len(src), length):
            s = src[i:i + length]
            hexa = " ".join(map("{0:0>2X}".format, src))
            text = "".join([chr(x) if 0x20 <= x < 0x7F else "." for x in s])
            result.append("%04X   %-*s   %s" % (i, length * (digits + 1), hexa, text))
        return "\n".join(result)

async def run(address, debug=False):
    if debug:
        import sys

        l = logging.getLogger("asyncio")
        l.setLevel(logging.DEBUG)
        h = logging.StreamHandler(sys.stdout)
        h.setLevel(logging.DEBUG)
        l.addHandler(h)
        logger.addHandler(h)



    async with BleakClient(address) as client:
        x = await client.is_connected()
        logger.info("Connected: {0}".format(x))

        bleDevice = client
        await client.start_notify(CHARACTERISTIC_UUID, notification_handler)


        # before: asyncio.sleep(5)


        # now: wait here until I the notification_hanlder get a callback, then do the write

        await client.write_gatt_char(CHARACTERISTIC_UUID_WR, [0xA6, 0x00, 0x02, 0xD0, 0x01, 0x77])
        
        await client.write_gatt_char(CHARACTERISTIC_UUID_WR, [0xA6])

        await client.write_gatt_char(CHARACTERISTIC_UUID_WR, [0xA7])

if __name__ == "__main__":
    import os

    os.environ["PYTHONASYNCIODEBUG"] = str(1)
    address = (
        "48:23:35:00:14:be"  # <--- Change to your device's address here if you are using Windows or Linux
        if platform.system() != "Darwin"
        else "B9EA5233-37EF-4DD6-87A8-2A875E821C46"  # <--- Change to your device's address here if you are using macOS
    )

    # for i in range(5):
    loop = asyncio.get_event_loop()
    loop.set_debug(True)
    loop.run_until_complete(run(address, True))