How to declare a uctypes.ARRAY for a string?

[brianreinhold]

From the documentation I cannot tell why this unit test is failing on the first ARRAY declaration case:

import unittest

import sys
sys.path.insert(1,"lni")

import bt_phd_info
import uctypes

phd_info_layout = {
    "addr_type": (uctypes.UINT8 | 0),        # Type of address (random ,public) Needed for the lower levels in the delete bonding
    "pairable": (uctypes.UINT8 | 1),         # Whether or not the device is pairable. For proprietary devices this information might be known.
    "bonded": (uctypes.UINT8 | 2),           # Whether or not the device is bonded. THis will always be False during discovery.
    "encrypted": (uctypes.UINT8 | 3),        # Whether or not the device connection is encrypted. Set to False at the start of every connection
    "connected": (uctypes.UINT8 | 4),        # Whether or not the device is connected. Need this since the aioble device state is too slow to get that
    "regulated": (uctypes.UINT8 | 5),        # Whether or not the device is regulated from the reg cert data list of the DIS or from proprietary information
    "battery_level": (uctypes.UINT8 | 6),    # Battery level in percent (Typcially from Battery Service)
    "bt_addr": (uctypes.ARRAY | 8, uctypes.UINT8 | 12),       # Bluetooth Address as HEX string without colons
    "device_name": (uctypes.ARRAY | 20, uctypes.UINT8 | 24),  # Device name (truncated to 16 characters)
    "system_id": (uctypes.ARRAY | 44, uctypes.UINT8 | 16),            # The EUI-64 system id
    "model_number": (uctypes.ARRAY | 60, uctypes.UINT8 | 16),         # Model number from DIS or equivalent
    "manufacturer": (uctypes.ARRAY | 76, uctypes.UINT8 | 24),         # Manufacturer name from DIS or equivalent
    "serial_number": (uctypes.ARRAY | 100, uctypes.UINT8 | 16),        # Serial number from DIS or equivalent
    "firmware_version": (uctypes.ARRAY | 116, uctypes.UINT8 | 16),    # Firmware version from DIS or equivalent
    "hardware_version": (uctypes.ARRAY | 132, uctypes.UINT8 | 16),    # Hardware version from DIS or equivalent
    "software_version": (uctypes.ARRAY | 148, uctypes.UINT8 | 16),    # Software version from DIS or equivalent
    "last_connected": (uctypes.ARRAY | 164, uctypes.UINT8 | 25),      # Time last connected. FHIR string 2024-06-07T13:25:38+00:00
    "welch_allyn_password": (uctypes.UINT32 | 192),                      # Stores the password from Welch allyn device set up
    "welch_allyn_account_id": (uctypes.ARRAY | 196, uctypes.UINT8 | 8)   # Welch allyn account id which is 8 digits
}


class TestUctypes(unittest.TestCase):

    def test_phd_info_layout_basic(self):
        print('started')
        size: int = uctypes.sizeof(phd_info_layout)
        self.assertEqual(size, 204)
        
        phdInfoBuffer: bytearray = bytearray(uctypes.sizeof(phd_info_layout))
        phdinfo_struct = uctypes.struct(uctypes.addressof(phdInfoBuffer), phd_info_layout)
        phdinfo_struct.addr_type = 0
        self.assertEqual(0, phdinfo_struct.addr_type)
        phdinfo_struct.bonded = True
        self.assertTrue(phdinfo_struct.bonded)
        phdinfo_struct.encrypted = False
        self.assertFalse(phdinfo_struct.encrypted)
        phdinfo_struct.connected = True
        self.assertTrue(phdinfo_struct.connected)
        phdinfo_struct.regulated = True
        self.assertTrue(phdinfo_struct.regulated)
        phdinfo_struct.battery_level = 90
        self.assertEqual(90, phdinfo_struct.battery_level)
        phdinfo_struct.bt_addr = bytearray('04af11c3de90'.encode('utf-8'))
        self.assertEqual('04af11c3de90', phdinfo_struct.bt_addr.decode('utf-8'))
        phdinfo_struct.serial_number = '452684DDF-g'.encode('utf-8')
        self.assertEqual('452684DDF-g', phdinfo_struct.serial_number.decode('utf-8'))
        
if __name__ == '__main__':
    unittest.main()
    

I have tried this

        phdinfo_struct.bt_addr = bytearray('04af11c3de90'.encode('utf-8'))
        self.assertEqual('04af11c3de90', phdinfo_struct.bt_addr.decode('utf-8'))

and this

        phdinfo_struct.bt_addr = '04af11c3de90'.encode('utf-8')
        self.assertEqual('04af11c3de90', phdinfo_struct.bt_addr.decode('utf-8'))

and they both give the same error

Traceback (most recent call last):
  File "/lib/unittest.py", line 213, in run_class
  File "test_uctypes.py", line 53, in test_phd_info_layout_basic
TypeError: syntax error in uctypes descriptor

Line 53 is phdinfo_struct.bt_addr = bytearray('04af11c3de90'.encode('utf-8'))
What am I doing wrong?

[brianreinhold]

I think I found an answer to this:
I have to do
phdinfo_struct.bt_addr[0 : 12] = '04af11c3de90'.encode('utf-8')
instead of
phdinfo_struct.bt_addr = '04af11c3de90'.encode('utf-8')

which means that I have to keep track of string lengths for those strings which are of variable lengths.

The approach works but if someone has a better way I would be happy to know it!