Add option to remove event handler from luigi.Task

luigi/task.py

@@ -264,6 +264,13 @@ def wrapped(callback):
             return callback
         return wrapped
 
+    @classmethod
+    def remove_event_handler(cls, event, callback):
+        """
+        Function to remove the event handler registered previously by the cls.event_handler decorator.
+        """
+        cls._event_callbacks[cls][event].remove(callback)
+
     def trigger_event(self, event, *args, **kwargs):
         """
         Trigger that calls all of the specified events associated with this class.

test/event_callbacks_test.py

@@ -162,6 +162,21 @@ def test_processing_time_handler_failure(self):
         t, result = self._run_processing_time_handler(True)
         self.assertEqual(result, [])
 
+    def test_remove_event_handler(self):
+        run_cnt = 0
+
+        @EmptyTask.event_handler(luigi.Event.START)
+        def handler(task):
+            nonlocal run_cnt
+            run_cnt += 1
+
+        task = EmptyTask()
+        build([task], local_scheduler=True)
+        assert run_cnt == 1
+        EmptyTask.remove_event_handler(luigi.Event.START, handler)
+        build([task], local_scheduler=True)
+        assert run_cnt == 1
+
 
 #        A
 #      /   \