Use a custom Exception instead of broad KeyError

Author: alexrudd2

pymodbus/datastore/store.py

@@ -51,7 +51,7 @@
 from collections.abc import Iterable
 from typing import Any, Generic, TypeVar
 
-from pymodbus.exceptions import ParameterException
+from pymodbus.exceptions import NoSuchAddressException, ParameterException
 
 
 # ---------------------------------------------------------------------------#
@@ -259,8 +259,12 @@ def getValues(self, address, count=1):
         :param address: The starting address
         :param count: The number of values to retrieve
         :returns: The requested values from a:a+c
+        :raises: NoSuchAddressException
         """
-        return [self.values[i] for i in range(address, address + count)]
+        try:
+            return [self.values[i] for i in range(address, address + count)]
+        except KeyError as e:
+            raise NoSuchAddressException(str(e)) from e
 
     def _process_values(self, values):
         """Process values."""

pymodbus/exceptions.py

@@ -69,6 +69,14 @@ def __init__(self, string=""):
         message = f"[No Such id] {string}"
         ModbusException.__init__(self, message)
 
+class NoSuchAddressException(ModbusException):
+    """Error resulting from making a request for a register that does not exist."""
+
+    def __init__(self, string=""):
+        """Initialize."""
+        message = f"[No such register address] {string}"
+        ModbusException.__init__(self, message)
+
 
 class NotImplementedException(ModbusException):
     """Error resulting from not implemented function."""

pymodbus/server/requesthandler.py

@@ -4,7 +4,11 @@
 import asyncio
 import traceback
 
-from pymodbus.exceptions import ModbusIOException, NoSuchIdException
+from pymodbus.exceptions import (
+    ModbusIOException,
+    NoSuchAddressException,
+    NoSuchIdException,
+)
 from pymodbus.logging import Log
 from pymodbus.pdu.pdu import ExceptionResponse
 from pymodbus.transaction import TransactionManager
@@ -105,7 +109,7 @@ async def handle_request(self):
             if self.server.ignore_missing_devices:
                 return  # the client will simply timeout waiting for a response
             response = ExceptionResponse(self.last_pdu.function_code, ExceptionResponse.GATEWAY_NO_RESPONSE)
-        except KeyError:
+        except NoSuchAddressException:
             Log.error("Requested register address does not exist: {}", self.last_pdu.address)
             response = ExceptionResponse(self.last_pdu.function_code, ExceptionResponse.ILLEGAL_ADDRESS)
         except Exception as exc:  # pylint: disable=broad-except