Raymond> Can we get most of the same benefit by using an assert() rather Raymond> than NULL-->SystemError? Jeremy> No. assert() causes the program to fail. SystemError() raises Jeremy> an exception and lets the program keep going. Those are vastly Jeremy> different effects. It's not clear to me that you'd see any benefit anyway. The checking code currently looks like this: if (o == NULL) return null_error(); If you changed it to use assert you'd have assert(o != NULL); which expands to ((o != NULL) ? 0 : __assert(...)); In the common case you still test for either o==NULL or o!=NULL. Unless one test is terrifically faster than the other (and you executed it a helluva lot) you wouldn't gain anything except the loss of the possibility (however slim) that you might be able to recover. Still, for people who's only desire is speed and are willing to sacrifice checks to get it, perhaps we should have a --without-null-checks configure flag. ;-) I bet if you were ruthless in eliminating checks (especially in ceval.c) you would see an easily measurable speedup. Skip