AttributeError: 'NoneType' object has no attribute 'scan' - bluetooth-lowenergy

Question

`I am trying to scan for devices advertising the UART service using Micropython on esp32. but I get AttributeError: 'NoneType' object has no attribute 'scan'
below is my code:
# Initialize and enable the BLE radio.
ble = ubluetooth.BLE()
ble.active(True)
# Create a BLE scanner object.
scanner = ble.gap_scan(10, 30000, 30000)
# Scan for devices advertising the UART service.
print('Scanning for devices advertising the UART service...')
devices = scanner.scan(10)
# Connect to the first device with the matching UART service UUID.
for device in devices:
for advertised_service in device.services:
if advertised_service.uuid == UART_SERVICE_UUID:
# Connect to the device.
print(f'Connecting to device {device.name}...')
connection = ble.connect(device)
# Wait for the connection to be established.
while not connection.is_connected:
pass
print('Connection established!')
# Stop scanning.
scanner.stop()
break
if connection.is_connected:
break
`

Answer 1

Your code reads:
# Create a BLE scanner object.
scanner = ble.gap_scan(10, 30000, 30000)
# Scan for devices advertising the UART service.
print('Scanning for devices advertising the UART service...')
devices = scanner.scan(10)
You're using the gap_scan() method incorrectly. According to the documentation, when the scanner detects a device it calls the callback function. You're getting an error because gap_scan() doesn't return anything, which is consistent with the documentation.
You need to register an event handler in order to see the results of a scan. So:
def ble_callback_handler(event, data):
if event == _IRQ_SCAN_RESULT:
# A single scan result. Do whatever you need with this
addr_type, addr, adv_type, rssi, adv_data = data
elif event == _IRQ_SCAN_DONE:
# Scan duration finished or manually stopped.
# register a callback handler
ble.irq(ble_callback_handler)
# start scanning
ble.gap_scan(10, 30000, 30000)