Add some type annotations for the nmt module (#586)

Co-authored-by: Erlend E. Aasland <erlend@python.org>

Author: acolomb

canopen/nmt.py

@@ -2,7 +2,7 @@
 import struct
 import threading
 import time
-from typing import Callable, Optional, TYPE_CHECKING
+from typing import Callable, Dict, Final, List, Optional, TYPE_CHECKING
 
 import canopen.network
 
@@ -12,7 +12,7 @@
 
 logger = logging.getLogger(__name__)
 
-NMT_STATES = {
+NMT_STATES: Final[Dict[int, str]] = {
     0: 'INITIALISING',
     4: 'STOPPED',
     5: 'OPERATIONAL',
@@ -21,7 +21,7 @@
     127: 'PRE-OPERATIONAL'
 }
 
-NMT_COMMANDS = {
+NMT_COMMANDS: Final[Dict[str, int]] = {
     'OPERATIONAL': 1,
     'STOPPED': 2,
     'SLEEP': 80,
@@ -32,7 +32,7 @@
     'RESET COMMUNICATION': 130
 }
 
-COMMAND_TO_STATE = {
+COMMAND_TO_STATE: Final[Dict[int, int]] = {
     1: 5,
     2: 4,
     80: 80,
@@ -117,7 +117,7 @@ def __init__(self, node_id: int):
         #: Timestamp of last heartbeat message
         self.timestamp: Optional[float] = None
         self.state_update = threading.Condition()
-        self._callbacks = []
+        self._callbacks: List[Callable[[int], None]] = []
 
     def on_heartbeat(self, can_id, data, timestamp):
         with self.state_update:
@@ -186,7 +186,8 @@ def start_node_guarding(self, period: float):
         :param period:
             Period (in seconds) at which the node guarding should be advertised to the slave node.
         """
-        if self._node_guarding_producer : self.stop_node_guarding()
+        if self._node_guarding_producer:
+            self.stop_node_guarding()
         self._node_guarding_producer = self.network.send_periodic(0x700 + self.id, None, period, True)
 
     def stop_node_guarding(self):