import subprocess
import time

# [!] To get this to work bluetoothctl needs to connect to the device before using BLE_GATT.connect
def ble_ctl(addr:str):
    """
    use bluetoothctl interactively: scan on, ... wait ..., scan off, connect CF:CD:27:79:55:6B, exit
    subprocess has a relevant bug in line-buffering, see issue 21471
    """
    ctl = subprocess.Popen(['bluetoothctl'], stdin = subprocess.PIPE)
    def writeHelper(proc, str, delay = 1):
        proc.stdin.write(str.encode('utf-8'))
        proc.stdin.flush()
        time.sleep(delay)
    # send bluetoothctl commands interactively
    writeHelper(ctl, "scan on\n", 4)
    writeHelper(ctl, "scan off\n")
    writeHelper(ctl, "connect " + addr + "\n", 3)
    writeHelper(ctl, "exit\n")
    # wait for child subprocess to terminate
    while True:
        if None != ctl.poll():
            break
        time.sleep(.1)

ble_ctl('CF:CD:27:79:55:6B')