On Linux, the following C program tells me that pthread_t is unsigned. --- #include <pthread.h> #include <stdio.h> #define TYPE_IS_SIGNED(TYPE) ((TYPE)-1 < (TYPE)0) int main() { printf("signed? %i\n", TYPE_IS_SIGNED(pthread_t)); return 0; } --- So it's fair to modify threading.get_ident() to return an unsigned number. But I disagree to change stable Python versions, it may break applications. Oh, I wrote write_thread_id() in Python/traceback.c and this function already casts the thread identifier to an unsigned number ;-)