Coding style.

- EXCEPTION is private.

fill3/fill3/__init__.py

@@ -409,7 +409,7 @@ class Fixed:
 ##########################
 
 
-EXCEPTION = None
+_EXCEPTION = None
 _LAST_APPEARANCE = []
 
 
@@ -418,8 +418,8 @@ def handle_exception(func):
         try:
             return func(*args)
         except Exception as exc:
-            global EXCEPTION
-            EXCEPTION = exc
+            global _EXCEPTION
+            _EXCEPTION = exc
             SHUTDOWN_EVENT.set()
     return wrapper
 
@@ -489,8 +489,8 @@ async def tui(title, screen_widget):
                 loop.remove_reader(sys.stdin)
         finally:
             update_task.cancel()
-    if EXCEPTION is not None:
-        raise EXCEPTION
+    if _EXCEPTION is not None:
+        raise _EXCEPTION
 
 ##########################