Implement helper to get all EventHandler instances in a given stack frame

lib/tfw/event_handler_base.py

@@ -2,6 +2,7 @@
 # All Rights Reserved. See LICENSE file for details.
 
 from abc import ABC, abstractmethod
+from inspect import currentframe
 
 from tfw.networking.event_handlers import ServerConnector
 from tfw.crypto import message_checksum, KeyManager, verify_message
@@ -105,6 +106,18 @@ class EventHandlerBase(ABC):
         """
         pass
 
+    @classmethod
+    def get_local_instances(cls):
+        frame = currentframe()
+        if frame is None:
+            raise EnvironmentError('inspect.currentframe() is not supported!')
+
+        locals_values = frame.f_back.f_locals.values()
+        return {
+            instance for instance in locals_values
+            if isinstance(instance, cls)
+        }
+
 
 class FSMAwareEventHandler(EventHandlerBase, ABC):
     # pylint: disable=abstract-method