It's INTERN_STRINGS. I'd like to get rid of it. Ditto DONT_SHARE_SHORT_STRINGS. Ditto CACHE_HASH and COUNT_ALLOCS, for that matter.
INTERN_STRINGS and CACHE_HASH should always be on (as they are by default).
DONT_SHARE_SHORT_STRINGS should always be off (as it is by default).
COUNT_ALLOCS should be on iff Py_TRACE_REFS is on (though currently it's always off).
I'd be happy to lose all 4 symbols.
--Guido van Rossum (home page: http://www.python.org/%7Eguido/)