SF bug #488687 reported by Neal Norwitz The error for assignment to __debug__ used ste->ste_opt_lineno instead of n->n_lineno. The latter was at best incorrect; often the slot was uninitialized. Two fixes here: Use the correct lineno for the error. Initialize ste_opt_lineno in PySymtable_New(); while there are no current cases where it is referenced unless it has already been assigned to, there is no harm in initializing it.