Experimental parser: some cleanup and assertions for rule_parser

tools/lexer_generator/regex_parser.py

 # Copyright 2013 the V8 project authors. All rights reserved.
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions are
 # met:
 #
 #     * Redistributions of source code must retain the above copyright
 #       notice, this list of conditions and the following disclaimer.
 #     * Redistributions in binary form must reproduce the above
 #       copyright notice, this list of conditions and the following
 #       disclaimer in the documentation and/or other materials provided
@@ skipping 140 matching lines @@
   __static_instance = None
   @staticmethod
   def parse(data):
     parser = RegexParser.__static_instance
     if not parser:
       parser = RegexParser()
       parser.build()
       RegexParser.__static_instance = parser
     try:
       return parser.parser.parse(data, lexer=parser.lexer.lexer)
-    except Exception as e:
+    except Exception:
       RegexParser.__static_instance = None
-      raise e
+      raise