implement Notifier.find_instance(bus)

can/notifier.py

@@ -50,12 +50,12 @@ def __init__(self) -> None:
     def register(self, bus: BusABC, notifier: "Notifier") -> None:
         """Register a bus and its associated notifier.
 
-        Ensures that a bus is not added to multiple active Notifier instances.
+        Ensures that a bus is not added to multiple active :class:`~can.Notifier` instances.
 
         :param bus:
             The CAN bus to register.
         :param notifier:
-            The Notifier instance associated with the bus.
+            The :class:`~can.Notifier` instance associated with the bus.
         :raises ValueError:
             If the bus is already assigned to an active Notifier.
         """
@@ -75,7 +75,7 @@ def unregister(self, bus: BusABC, notifier: "Notifier") -> None:
         :param bus:
             The CAN bus to unregister.
         :param notifier:
-            The Notifier instance associated with the bus.
+            The :class:`~can.Notifier` instance associated with the bus.
         """
         with self.lock:
             registered_pairs_to_remove: List[_BusNotifierPair] = []
@@ -85,6 +85,26 @@ def unregister(self, bus: BusABC, notifier: "Notifier") -> None:
             for pair in registered_pairs_to_remove:
                 self.pairs.remove(pair)
 
+    def find_instance(self, bus: BusABC) -> Optional["Notifier"]:
+        """Find the :class:`~can.Notifier` instance associated with a given CAN bus.
+
+        This method searches the registry for the :class:`~can.Notifier`
+        that is linked to the specified bus. If the bus is found, the
+        corresponding :class:`~can.Notifier` instance is returned. If the bus is not
+        found in the registry, `None` is returned.
+
+        :param bus:
+            The CAN bus for which to find the associated :class:`~can.Notifier` .
+        :return:
+            The :class:`~can.Notifier` instance associated with the given bus,
+            or `None` if no such association exists.
+        """
+        with self.lock:
+            for pair in self.pairs:
+                if bus is pair.bus:
+                    return pair.notifier
+        return None
+
 
 class Notifier(AbstractContextManager):
 
@@ -274,6 +294,23 @@ def stopped(self) -> bool:
         """Return ``True``, if Notifier was properly shut down with :meth:`~can.Notifier.stop`."""
         return self._stopped
 
+    @classmethod
+    def find_instance(cls, bus: BusABC) -> Optional["Notifier"]:
+        """Find the :class:`~can.Notifier` instance associated with a given CAN bus.
+
+        This method searches the registry for the :class:`~can.Notifier`
+        that is linked to the specified bus. If the bus is found, the
+        corresponding :class:`~can.Notifier` instance is returned. If the bus is not
+        found in the registry, `None` is returned.
+
+        :param bus:
+            The CAN bus for which to find the associated :class:`~can.Notifier` .
+        :return:
+            The :class:`~can.Notifier` instance associated with the given bus,
+            or `None` if no such association exists.
+        """
+        return cls._registry.find_instance(bus)
+
     def __exit__(
         self,
         exc_type: Optional[Type[BaseException]],

test/notifier_test.py

@@ -52,15 +52,24 @@ def test_context_manager(self):
     def test_registry(self):
         with can.Bus("test", interface="virtual", receive_own_messages=True) as bus:
             reader = can.BufferedReader()
-            with can.Notifier(bus, [reader], 0.1):
+            with can.Notifier(bus, [reader], 0.1) as notifier:
                 # creating a second notifier for the same bus must fail
                 self.assertRaises(ValueError, can.Notifier, bus, [reader], 0.1)
 
+                # find_instance must return the existing instance
+                self.assertIs(can.Notifier.find_instance(bus), notifier)
+
+            # Notifier is stopped, find instance must return None
+            self.assertIsNone(can.Notifier.find_instance(bus))
+
             # now the first notifier is stopped, a new notifier can be created without error:
-            with can.Notifier(bus, [reader], 0.1):
+            with can.Notifier(bus, [reader], 0.1) as notifier:
                 # the next notifier call should fail again since there is an active notifier already
                 self.assertRaises(ValueError, can.Notifier, bus, [reader], 0.1)
 
+                # find_instance must return the existing instance
+                self.assertIs(can.Notifier.find_instance(bus), notifier)
+
 
 class AsyncNotifierTest(unittest.TestCase):
     def test_asyncio_notifier(self):