Unhashable type for Systec interface errors

Traceback:

Traceback (most recent call last):
  File "c:\Users\thoma\OneDrive\Documents\Tyto\Python scripts\test.py", line 51, in <module>
    dc_node.spin(timeout=0.001)
  File "C:\Python310\lib\site-packages\dronecan\node.py", line 439, in spin
    execute_once()
  File "C:\Python310\lib\site-packages\dronecan\node.py", line 431, in execute_once
    frame = self._can_driver.receive(read_timeout)
  File "C:\Python310\lib\site-packages\dronecan\driver\python_can.py", line 137, in receive
    self._check_write_feedback()
  File "C:\Python310\lib\site-packages\dronecan\driver\python_can.py", line 124, in _check_write_feedback
    raise item
  File "C:\Python310\lib\site-packages\dronecan\driver\python_can.py", line 101, in _writer_thread_loop
    self._bus.send(msg)
  File "C:\Python310\lib\site-packages\can\interfaces\systec\ucanbus.py", line 212, in send
    self._ucan.write_can_msg(self.channel, [message])
  File "C:\Python310\lib\site-packages\can\interfaces\systec\ucan.py", line 488, in write_can_msg
    UcanWriteCanMsgEx(self._handle, channel, c_can_msg, c_count)
  File "C:\Python310\lib\site-packages\can\interfaces\systec\ucan.py", line 109, in check_result
    raise UcanError(result, func, arguments)
  File "C:\Python310\lib\site-packages\can\interfaces\systec\exceptions.py", line 16, in __init__
    message = self._error_message_mapping.get(result, "unknown")
TypeError: unhashable type

Script to recreate the bug:

import can
import dronecan
from dronecan.driver import python_can as pycan_driver
from dronecan.app.node_monitor import NodeMonitor
import time

can_bus = pycan_driver.PythonCAN(channel=0, interface="systec", bustype="systec", bitrate=1000000)

node_id = 45

dc_node = dronecan.node.Node(can_bus, node_id=node_id, bitrate=1000000)

print("=== Local Node ===")
print(f"  node_id : {dc_node.node_id}")
print(f"  mode    : {dc_node.mode}")
print(f"  health  : {dc_node.health}")
print()

# Print every NodeStatus as it is received:

def on_node_status(event):

    print(
        f"[NodeStatus] from node {event.transfer.source_node_id}: "
        f"uptime={event.message.uptime_sec}s "
        f"health={event.message.health} "
        f"mode={event.message.mode}"
    )
 
dc_node.add_handler(dronecan.uavcan.protocol.NodeStatus, on_node_status)

LISTEN_SECONDS = 10

monitor = NodeMonitor(dc_node)

print(f"Listening for {LISTEN_SECONDS} seconds...\n")
deadline = time.monotonic() + LISTEN_SECONDS
while time.monotonic() < deadline:
    try:
        dc_node.spin(timeout=0.001)
        msg = dronecan.uavcan.equipment.esc.RPMCommand()
        msg.cmd = int(0)
        dc_node.broadcast(msg)
    except dronecan.transport.TransferError as ex:
        print(f"  (transfer error, continuing: {ex})")

dc_node.close()

With Claude, I tracked down the error to interfaces/systec/exceptions.py. A ctypes.c_ubyte error code is passed to the Python interface, and the systec backend fails to interpret it. By changing Line 16 in exceptions.py, I can see the underlying exception and original error message:

message = self._error_message_mapping.get(result, "unknown")

should become

message = self._error_message_mapping.get(result.value, "unknown")

This seems to have solved the issue, and now I can troubleshoot my hardware problems better. I cannot make a PR for this at the moment, but I might later.