Nevermind my previous question. I found the answer in "Learning Python"
>> Python internally caches and reuses short strings as an optimization, there really is just a single string, 'spam', in memory, shared by S1 and S2; hence, the is identity test reports a true result. To trigger the normal behavior, we need to use longer strings that fall outside the cache mechanism: << -- http://mail.python.org/mailman/listinfo/python-list
