diff --git a/Python/ceval.c b/Python/ceval.c
index 50ea9c3..6985846 100644
--- a/Python/ceval.c
+++ b/Python/ceval.c
@@ -51,6 +51,9 @@
 static void call_trace_protected(Py_tracefunc, PyObject *,
 				 PyFrameObject *, int);
 static void call_exc_trace(Py_tracefunc, PyObject *, PyFrameObject *);
+static void maybe_call_line_trace(int, Py_tracefunc, PyObject *, 
+				  PyFrameObject *, int *, int *);
+
 static PyObject *apply_slice(PyObject *, PyObject *, PyObject *);
 static int assign_slice(PyObject *, PyObject *,
 			PyObject *, PyObject *);
@@ -499,6 +502,16 @@
 	PyObject *retval = NULL;	/* Return value */
 	PyThreadState *tstate = PyThreadState_GET();
 	PyCodeObject *co;
+
+	/* when tracing we set things up so that 
+
+               not (instr_lb <= current_bytecode_offset < instr_ub)
+
+	   is true when the line being executed has changed.  The 
+           initial values are such as to make this false the first
+           time it is tested. */
+	int instr_ub = -1, instr_lb = 0;
+
 	unsigned char *first_instr;
 	PyObject *names;
 	PyObject *consts;
@@ -586,7 +599,12 @@
 	fastlocals = f->f_localsplus;
 	freevars = f->f_localsplus + f->f_nlocals;
 	_PyCode_GETCODEPTR(co, &first_instr);
-	next_instr = first_instr + f->f_lasti;
+	if (f->f_lasti < 0) {
+		next_instr = first_instr;
+	}
+	else {
+		next_instr = first_instr + f->f_lasti;
+	}
 	stack_pointer = f->f_stacktop;
 	assert(stack_pointer != NULL);
 	f->f_stacktop = NULL;	/* remains NULL unless yield suspends frame */
@@ -637,8 +655,9 @@
 	w = NULL;
 
 	for (;;) {
-		assert(stack_pointer >= f->f_valuestack);	/* else underflow */
-		assert(STACK_LEVEL() <= f->f_stacksize);	/* else overflow */
+		assert(stack_pointer >= f->f_valuestack); /* else underflow */
+		assert(STACK_LEVEL() <= f->f_stacksize);  /* else overflow */
+
 		/* Do periodic things.  Doing this every time through
 		   the loop would add too much overhead, so we do it
 		   only every Nth instruction.  We also do it if
@@ -658,8 +677,8 @@
 #if !defined(HAVE_SIGNAL_H) || defined(macintosh)
 			/* If we have true signals, the signal handler
 			   will call Py_AddPendingCall() so we don't
-			   have to call sigcheck().  On the Mac and
-			   DOS, alas, we have to call it. */
+			   have to call PyErr_CheckSignals().  On the 
+			   Mac and DOS, alas, we have to call it. */
 			if (PyErr_CheckSignals()) {
 				why = WHY_EXCEPTION;
 				goto on_error;
@@ -686,9 +705,7 @@
 	fast_next_opcode:
 		/* Extract opcode and argument */
 
-#if defined(Py_DEBUG) || defined(LLTRACE)
 		f->f_lasti = INSTR_OFFSET();
-#endif
 
 		opcode = NEXTOP();
 		if (HAS_ARG(opcode))
@@ -708,15 +725,26 @@
 		if (lltrace) {
 			if (HAS_ARG(opcode)) {
 				printf("%d: %d, %d\n",
-					(int) (INSTR_OFFSET() - 3),
-					opcode, oparg);
+				       f->f_lasti, opcode, oparg);
 			}
 			else {
 				printf("%d: %d\n",
-					(int) (INSTR_OFFSET() - 1), opcode);
+				       f->f_lasti, opcode);
 			}
 		}
 #endif
+
+		/* line-by-line tracing support */
+
+		if (tstate->c_tracefunc != NULL && !tstate->tracing) {
+			/* see maybe_call_line_trace
+			   for expository comments */
+			maybe_call_line_trace(opcode, 
+					      tstate->c_tracefunc,
+					      tstate->c_traceobj,
+					      f, &instr_lb, &instr_ub);
+		}
+
 		/* Main switch on opcode */
 
 		switch (opcode) {
@@ -728,26 +756,6 @@
 
 		/* case STOP_CODE: this is an error! */
 
-		case SET_LINENO:
-#ifdef LLTRACE
-			if (lltrace)
-				printf("--- %s:%d \n", filename, oparg);
-#endif
-			f->f_lineno = oparg;
-			if (tstate->c_tracefunc == NULL || tstate->tracing)
-				goto fast_next_opcode;
-			/* Trace each line of code reached */
-			f->f_lasti = INSTR_OFFSET();
-			/* Inline call_trace() for performance: */
-			tstate->tracing++;
-			tstate->use_tracing = 0;
-			err = (tstate->c_tracefunc)(tstate->c_traceobj, f,
-						    PyTrace_LINE, Py_None);
-			tstate->use_tracing = (tstate->c_tracefunc
-					       || tstate->c_profilefunc);
-			tstate->tracing--;
-			break;
-
 		case LOAD_FAST:
 			x = GETLOCAL(oparg);
 			if (x != NULL) {
@@ -1504,9 +1512,17 @@
 			why = WHY_RETURN;
 			break;
 
+		case RETURN_NONE:
+			retval = Py_None;
+			Py_INCREF(retval);
+			why = WHY_RETURN;
+			break;
+
 		case YIELD_VALUE:
 			retval = POP();
 			f->f_stacktop = stack_pointer;
+			/* abuse the lasti field: here it points to 
+			   the *next* instruction */
 			f->f_lasti = INSTR_OFFSET();
 			why = WHY_YIELD;
 			break;
@@ -1954,7 +1970,6 @@
 		    int n = na + 2 * nk;
 		    PyObject **pfunc = stack_pointer - n - 1;
 		    PyObject *func = *pfunc;
-		    f->f_lasti = INSTR_OFFSET() - 3; /* For tracing */
 
 		    /* Always dispatch PyCFunction first, because
 		       these are presumed to be the most frequent
@@ -2022,7 +2037,6 @@
 			    n++;
 		    pfunc = stack_pointer - n - 1;
 		    func = *pfunc;
-		    f->f_lasti = INSTR_OFFSET() - 3; /* For tracing */
 
 		    if (PyMethod_Check(func)
 			&& PyMethod_GET_SELF(func) != NULL) {
@@ -2134,7 +2148,8 @@
 		default:
 			fprintf(stderr,
 				"XXX lineno: %d, opcode: %d\n",
-				f->f_lineno, opcode);
+				PyCode_Addr2Line(f->f_code, f->f_lasti),
+				opcode);
 			PyErr_SetString(PyExc_SystemError, "unknown opcode");
 			why = WHY_EXCEPTION;
 			break;
@@ -2189,9 +2204,6 @@
 		/* Log traceback info if this is a real exception */
 
 		if (why == WHY_EXCEPTION) {
-			f->f_lasti = INSTR_OFFSET() - 1;
-			if (HAS_ARG(opcode))
-				f->f_lasti -= 2;
 			PyTraceBack_Here(f);
 
 			if (tstate->c_tracefunc != NULL)
@@ -2875,6 +2887,125 @@
 	return result;
 }
 
+static void
+maybe_call_line_trace(int opcode, Py_tracefunc func, PyObject *obj, 
+		      PyFrameObject *frame, int *instr_lb, int *instr_ub)
+{
+	/* The theory of SET_LINENO-less tracing.
+	   
+	   In a nutshell, we use the co_lnotab field of the code object
+	   to tell when execution has moved onto a different line.
+
+	   As mentioned above, the basic idea is so set things up so
+	   that
+
+	         *instr_lb <= frame->f_lasti < *instr_ub
+
+	   is true so long as execution does not change lines.
+
+	   This is all fairly simple.  Digging the information out of
+	   co_lnotab takes some work, but is conceptually clear.
+
+	   Somewhat harder to explain is why we don't call the line
+	   trace function when executing a POP_TOP or RETURN_NONE
+	   opcodes.  An example probably serves best.
+
+	   Consider this code:
+
+	   1: def f(a):
+	   2:     if a:
+	   3:        print 1
+	   4:     else:
+	   5:        print 2
+
+	   which compiles to this:
+
+	   2           0 LOAD_FAST                0 (a)
+		       3 JUMP_IF_FALSE            9 (to 15)
+		       6 POP_TOP             
+
+	   3           7 LOAD_CONST               1 (1)
+		      10 PRINT_ITEM          
+		      11 PRINT_NEWLINE       
+		      12 JUMP_FORWARD             6 (to 21)
+		 >>   15 POP_TOP             
+
+	   5          16 LOAD_CONST               2 (2)
+		      19 PRINT_ITEM          
+		      20 PRINT_NEWLINE       
+		 >>   21 RETURN_NONE         
+
+	   If a is false, execution will jump to instruction at offset
+	   15 and the co_lnotab will claim that execution has moved to
+	   line 3.  This is at best misleading.  In this case we could
+	   associate the POP_TOP with line 4, but that doesn't make
+	   sense in all cases (I think).
+
+	   On the other hand, if a is true, execution will jump from
+	   instruction offset 12 to offset 21.  Then the co_lnotab would
+	   imply that execution has moved to line 5, which is again
+	   misleading.
+
+	   This is why it is important that RETURN_NONE is *only* used
+	   for the "falling off the end of the function" form of
+	   returning None -- using it for code like
+
+	   1: def f():
+	   2:     return
+
+	   would, once again, lead to misleading tracing behaviour.
+
+	   It is also worth mentioning that getting tracing behaviour
+	   right is the *entire* motivation for adding the RETURN_NONE
+	   opcode.
+	*/
+
+	if (opcode != POP_TOP && opcode != RETURN_NONE &&
+	    (frame->f_lasti < *instr_lb || frame->f_lasti > *instr_ub)) {
+		PyCodeObject* co = frame->f_code;
+		int size, addr;
+		unsigned char* p;
+
+		call_trace(func, obj, frame, PyTrace_LINE, Py_None);
+
+		size = PyString_Size(co->co_lnotab) / 2;
+		p = (unsigned char*)PyString_AsString(co->co_lnotab);
+
+		/* possible optimization: if f->f_lasti == instr_ub
+		   (likely to be a common case) then we already know
+		   instr_lb -- if we stored the matching value of p
+		   somwhere we could skip the first while loop. */
+
+		addr = 0;
+
+		/* see comments in compile.c for the description of
+		   co_lnotab.  A point to remember: increments to p
+		   should come in pairs -- although we don't care about
+		   the line increments here, treating them as byte
+		   increments gets confusing, to say the least. */
+
+		while (size >= 0) {
+			if (addr + *p > frame->f_lasti)
+				break;
+			addr += *p++;
+			p++;
+			--size;
+		}
+		*instr_lb = addr;
+		if (size > 0) {
+			while (--size >= 0) {
+				addr += *p++;
+				if (*p++)
+					break;
+			}
+			*instr_ub = addr;
+		}
+		else {
+			*instr_ub = INT_MAX;
+		}
+	}
+}
+
 void
 PyEval_SetProfile(Py_tracefunc func, PyObject *arg)
 {
diff --git a/Python/compile.c b/Python/compile.c
index 5b4e8e6..ff8f4a5 100644
--- a/Python/compile.c
+++ b/Python/compile.c
@@ -407,9 +407,10 @@
 
 /* All about c_lnotab.
 
-c_lnotab is an array of unsigned bytes disguised as a Python string.  In -O
-mode, SET_LINENO opcodes aren't generated, and bytecode offsets are mapped
-to source code line #s (when needed for tracebacks) via c_lnotab instead.
+c_lnotab is an array of unsigned bytes disguised as a Python string.  Since
+version 2.3, SET_LINENO opcodes are never generated and bytecode offsets are
+mapped to source code line #s via c_lnotab instead.
+
 The array is conceptually a list of
     (bytecode offset increment, line number increment)
 pairs.  The details are important and delicate, best illustrated by example:
@@ -830,11 +831,6 @@
 com_addoparg(struct compiling *c, int op, int arg)
 {
 	int extended_arg = arg >> 16;
-	if (op == SET_LINENO) {
-		com_set_lineno(c, arg);
-		if (Py_OptimizeFlag)
-			return;
-	}
 	if (extended_arg){
 		com_addbyte(c, EXTENDED_ARG);
 		com_addint(c, extended_arg);
@@ -1738,7 +1734,7 @@
 			  break;
 			if (ch->n_lineno != lineno) {
 				lineno = ch->n_lineno;
-				com_addoparg(c, SET_LINENO, lineno);
+				com_set_lineno(c, lineno);
 			}
 			com_argument(c, ch, &keywords);
 			if (keywords == NULL)
@@ -3168,7 +3164,7 @@
 			continue;
 		}
 		if (i > 0)
-			com_addoparg(c, SET_LINENO, ch->n_lineno);
+			com_set_lineno(c, ch->n_lineno);
 		com_node(c, ch);
 		com_addfwref(c, JUMP_IF_FALSE, &a);
 		com_addbyte(c, POP_TOP);
@@ -3195,7 +3191,7 @@
 	com_addfwref(c, SETUP_LOOP, &break_anchor);
 	block_push(c, SETUP_LOOP);
 	c->c_begin = c->c_nexti;
-	com_addoparg(c, SET_LINENO, n->n_lineno);
+	com_set_lineno(c, n->n_lineno);
 	com_node(c, CHILD(n, 1));
 	com_addfwref(c, JUMP_IF_FALSE, &anchor);
 	com_addbyte(c, POP_TOP);
@@ -3228,7 +3224,7 @@
 	com_node(c, CHILD(n, 3));
 	com_addbyte(c, GET_ITER);
 	c->c_begin = c->c_nexti;
-	com_addoparg(c, SET_LINENO, n->n_lineno);
+	com_set_lineno(c, n->n_lineno);
 	com_addfwref(c, FOR_ITER, &anchor);
 	com_push(c, 1);
 	com_assign(c, CHILD(n, 1), OP_ASSIGN, NULL);
@@ -3339,7 +3335,7 @@
 		}
 		except_anchor = 0;
 		com_push(c, 3); /* tb, val, exc pushed by exception */
-		com_addoparg(c, SET_LINENO, ch->n_lineno);
+		com_set_lineno(c, ch->n_lineno);
 		if (NCH(ch) > 1) {
 			com_addbyte(c, DUP_TOP);
 			com_push(c, 1);
@@ -3401,7 +3397,7 @@
 	com_push(c, 3);
 	com_backpatch(c, finally_anchor);
 	ch = CHILD(n, NCH(n)-1);
-	com_addoparg(c, SET_LINENO, ch->n_lineno);
+	com_set_lineno(c, ch->n_lineno);
 	com_node(c, ch);
 	com_addbyte(c, END_FINALLY);
 	block_pop(c, END_FINALLY);
@@ -3727,7 +3723,7 @@
 
 	case simple_stmt:
 		/* small_stmt (';' small_stmt)* [';'] NEWLINE */
-		com_addoparg(c, SET_LINENO, n->n_lineno);
+		com_set_lineno(c, n->n_lineno);
 		{
 			int i;
 			for (i = 0; i < NCH(n)-1; i += 2)
@@ -3736,7 +3732,7 @@
 		break;
 	
 	case compound_stmt:
-		com_addoparg(c, SET_LINENO, n->n_lineno);
+		com_set_lineno(c, n->n_lineno);
 		n = CHILD(n, 0);
 		goto loop;
 
@@ -3990,10 +3986,7 @@
 	c->c_infunction = 1;
 	com_node(c, CHILD(n, 4));
 	c->c_infunction = 0;
-	com_addoparg(c, LOAD_CONST, com_addconst(c, Py_None));
-	com_push(c, 1);
-	com_addbyte(c, RETURN_VALUE);
-	com_pop(c, 1);
+	com_addbyte(c, RETURN_NONE);
 }
 
 static void
@@ -4050,7 +4043,7 @@
 static void
 compile_node(struct compiling *c, node *n)
 {
-	com_addoparg(c, SET_LINENO, n->n_lineno);
+	com_set_lineno(c, n->n_lineno);
 	
 	switch (TYPE(n)) {
 	
@@ -4060,19 +4053,13 @@
 		n = CHILD(n, 0);
 		if (TYPE(n) != NEWLINE)
 			com_node(c, n);
-		com_addoparg(c, LOAD_CONST, com_addconst(c, Py_None));
-		com_push(c, 1);
-		com_addbyte(c, RETURN_VALUE);
-		com_pop(c, 1);
+		com_addbyte(c, RETURN_NONE);
 		c->c_interactive--;
 		break;
 	
 	case file_input: /* A whole file, or built-in function exec() */
 		com_file_input(c, n);
-		com_addoparg(c, LOAD_CONST, com_addconst(c, Py_None));
-		com_push(c, 1);
-		com_addbyte(c, RETURN_VALUE);
-		com_pop(c, 1);
+		com_addbyte(c, RETURN_NONE);
 		break;
 	
 	case eval_input: /* Built-in function input() */
diff --git a/Python/frozen.c b/Python/frozen.c
index 069ce3c..946d626 100644
--- a/Python/frozen.c
+++ b/Python/frozen.c
@@ -13,12 +13,12 @@
 
 static unsigned char M___hello__[] = {
 	99,0,0,0,0,0,0,0,0,1,0,0,0,0,0,0,
-	0,115,15,0,0,0,127,0,0,127,1,0,100,0,0,71,
-	72,100,1,0,83,40,2,0,0,0,115,14,0,0,0,72,
-	101,108,108,111,32,119,111,114,108,100,46,46,46,78,40,0,
-	0,0,0,40,0,0,0,0,40,0,0,0,0,40,0,0,
-	0,0,115,8,0,0,0,104,101,108,108,111,46,112,121,115,
-	1,0,0,0,63,1,0,0,0,115,0,0,0,0,
+	0,115,9,0,0,0,100,0,0,71,72,100,1,0,83,40,
+	2,0,0,0,115,14,0,0,0,72,101,108,108,111,32,119,
+	111,114,108,100,46,46,46,78,40,0,0,0,0,40,0,0,
+	0,0,40,0,0,0,0,40,0,0,0,0,115,8,0,0,
+	0,104,101,108,108,111,46,112,121,115,1,0,0,0,63,1,
+	0,0,0,115,0,0,0,0,
 };
 
 #define SIZE (int)sizeof(M___hello__)
diff --git a/Python/import.c b/Python/import.c
index 6fd05d8..36ca705 100644
--- a/Python/import.c
+++ b/Python/import.c
@@ -49,6 +49,9 @@
        algorithm relying on the above scheme. Perhaps we should simply
        start counting in increments of 10 from now on ?!
 
+       MWH, 2002-08-03: Removed SET_LINENO.  Couldn't be bothered figuring
+       out the MAGIC schemes, so just incremented it by 10.
+
    Known values:
        Python 1.5:   20121
        Python 1.5.1: 20121
@@ -60,8 +63,9 @@
        Python 2.1.2: 60202
        Python 2.2:   60717
        Python 2.3a0: 62011
+       Python 2.3a0: 62021
 */
-#define MAGIC (62011 | ((long)'\r'<<16) | ((long)'\n'<<24))
+#define MAGIC (62021 | ((long)'\r'<<16) | ((long)'\n'<<24))
 
 /* Magic word as global; note that _PyImport_Init() can change the
    value of this global to accommodate for alterations of how the
diff --git a/Python/traceback.c b/Python/traceback.c
index de918f9..27c69b6 100644
--- a/Python/traceback.c
+++ b/Python/traceback.c
@@ -103,8 +103,7 @@
 };
 
 static tracebackobject *
-newtracebackobject(tracebackobject *next, PyFrameObject *frame, int lasti,
-		   int lineno)
+newtracebackobject(tracebackobject *next, PyFrameObject *frame)
 {
 	tracebackobject *tb;
 	if ((next != NULL && !PyTraceBack_Check(next)) ||
@@ -118,8 +117,9 @@
 		tb->tb_next = next;
 		Py_XINCREF(frame);
 		tb->tb_frame = frame;
-		tb->tb_lasti = lasti;
-		tb->tb_lineno = lineno;
+		tb->tb_lasti = frame->f_lasti;
+		tb->tb_lineno = PyCode_Addr2Line(frame->f_code, 
+						 frame->f_lasti);
 		PyObject_GC_Track(tb);
 	}
 	return tb;
@@ -130,8 +130,7 @@
 {
 	PyThreadState *tstate = frame->f_tstate;
 	tracebackobject *oldtb = (tracebackobject *) tstate->curexc_traceback;
-	tracebackobject *tb = newtracebackobject(oldtb,
-				frame, frame->f_lasti, frame->f_lineno);
+	tracebackobject *tb = newtracebackobject(oldtb, frame);
 	if (tb == NULL)
 		return -1;
 	tstate->curexc_traceback = (PyObject *)tb;