Python 2.7 uses its own implementation of Thread Local Storage: see find_key() in Python/thread.c. This implementation uses a lock and a chained list. A fork only clones the current thread in the child process, all other threads are "removed", so Python has to manually remove all TLS variables of the other threads using PyThread_ReInitTLS().

I don't think that Python 3 is affected by such bug, since Python 3 uses native TLS APIs like pthread pthread_{get,set}specific() on UNIX/BSD.