Clarify the expanded code -- exc is just used as a flag.

pep-0343.txt

@@ -228,17 +228,19 @@ Specification: The 'with' Statement
         ctx = (EXPR).__context__()
         exit = exc.__exit__  # Not calling it yet
         value = ctx.__enter__()
-        exc = (None, None, None)
+        exc = True
         try:
             try:
                 VAR = value  # Only if "as VAR" is present
                 BLOCK
             except:
-                exc = None
+                # The exceptional case is handled here
+                exc = False
                 exit(*sys.exc_info())
         finally:
+            # The normal and non-local-goto cases are handled here
             if exc:
-                exit(*exc)
+                exit(None, None, None)
 
     Here, the lowercase variables (ctx, exit, value, exc) are internal
     variables and not accessible to the user; they will most likely be