Fix SYSTEC error lookup for ctypes result codes

can/interfaces/systec/exceptions.py

@@ -13,7 +13,7 @@ def __init__(self, result, func, arguments):
         self.func = func
         self.arguments = arguments
 
-        message = self._error_message_mapping.get(result, "unknown")
+        message = self._error_message_mapping.get(result.value, "unknown")
         super().__init__(
             message=f"Function {func.__name__} (called with {arguments}): {message}",
             error_code=result.value,

test/test_systec_exceptions.py

@@ -0,0 +1,16 @@
+from ctypes import c_ubyte
+
+from can.interfaces.systec.constants import ReturnCode
+from can.interfaces.systec.exceptions import UcanError
+
+
+def test_ucan_error_accepts_ctypes_result_code() -> None:
+    def ucan_write_can_msg_ex() -> None:
+        pass
+
+    result = c_ubyte(ReturnCode.ERR_ILLPARAM)
+
+    error = UcanError(result, ucan_write_can_msg_ex, ("arg",))
+
+    assert error.error_code == ReturnCode.ERR_ILLPARAM
+    assert "wrong parameter handed over to the function" in str(error)