Python/ceval.c

/***********************************************************
Copyright 1991, 1992 by Stichting Mathematisch Centrum, Amsterdam, The
Netherlands.

                        All Rights Reserved

Permission to use, copy, modify, and distribute this software and its 
documentation for any purpose and without fee is hereby granted, 
provided that the above copyright notice appear in all copies and that
both that copyright notice and this permission notice appear in 
supporting documentation, and that the names of Stichting Mathematisch
Centrum or CWI not be used in advertising or publicity pertaining to
distribution of the software without specific, written prior permission.

STICHTING MATHEMATISCH CENTRUM DISCLAIMS ALL WARRANTIES WITH REGARD TO
THIS SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND
FITNESS, IN NO EVENT SHALL STICHTING MATHEMATISCH CENTRUM BE LIABLE
FOR ANY SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT
OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.

******************************************************************/

/* Execute compiled code */

#include "allobjects.h"

#include "import.h"
#include "sysmodule.h"
#include "compile.h"
#include "frameobject.h"
#include "eval.h"
#include "ceval.h"
#include "opcode.h"
#include "bltinmodule.h"
#include "traceback.h"

/* Turn this on if your compiler chokes on the big switch: */
/* #define CASE_TOO_BIG 1 /**/

#ifndef NDEBUG
/* For debugging the interpreter: */
#define LLTRACE  1	/* Low-level trace feature */
#define CHECKEXC 1	/* Double-check exception checking */
#endif

/* Forward declarations */

#ifdef LLTRACE
static int prtrace PROTO((object *, char *));
#endif
static void call_exc_trace PROTO((object **, object**, frameobject *));
static int call_trace
	PROTO((object **, object **, frameobject *, char *, object *));
static int testbool PROTO((object *));
static object *add PROTO((object *, object *));
static object *sub PROTO((object *, object *));
static object *mul PROTO((object *, object *));
static object *divide PROTO((object *, object *));
static object *rem PROTO((object *, object *));
static object *neg PROTO((object *));
static object *pos PROTO((object *));
static object *not PROTO((object *));
static object *invert PROTO((object *));
static object *lshift PROTO((object *, object *));
static object *rshift PROTO((object *, object *));
static object *and PROTO((object *, object *));
static object *xor PROTO((object *, object *));
static object *or PROTO((object *, object *));
static object *call_builtin PROTO((object *, object *));
static object *call_function PROTO((object *, object *));
static object *apply_subscript PROTO((object *, object *));
static object *loop_subscript PROTO((object *, object *));
static int slice_index PROTO((object *, int, int *));
static object *apply_slice PROTO((object *, object *, object *));
static int assign_subscript PROTO((object *, object *, object *));
static int assign_slice PROTO((object *, object *, object *, object *));
static int cmp_exception PROTO((object *, object *));
static int cmp_member PROTO((object *, object *));
static object *cmp_outcome PROTO((int, object *, object *));
static int import_from PROTO((object *, object *, object *));
static object *build_class PROTO((object *, object *));


/* Pointer to current frame, used to link new frames to */

static frameobject *current_frame;

#ifdef USE_THREAD

#include <errno.h>
#include "thread.h"

static type_lock interpreter_lock;

void
init_save_thread()
{
	if (interpreter_lock)
		fatal("2nd call to init_save_thread");
	interpreter_lock = allocate_lock();
	acquire_lock(interpreter_lock, 1);
}

#endif

/* Functions save_thread and restore_thread are always defined so
   dynamically loaded modules needn't be compiled separately for use
   with and without threads: */

object *
save_thread()
{
#ifdef USE_THREAD
	if (interpreter_lock) {
		object *res;
		res = (object *)current_frame;
		current_frame = NULL;
		release_lock(interpreter_lock);
		return res;
	}
	else
		return NULL;
#endif
}

void
restore_thread(x)
	object *x;
{
#ifdef USE_THREAD
	if (interpreter_lock) {
		int err;
		err = errno;
		acquire_lock(interpreter_lock, 1);
		errno = err;
		current_frame = (frameobject *)x;
	}
#endif
}


/* Status code for main loop (reason for stack unwind) */

enum why_code {
		WHY_NOT,	/* No error */
		WHY_EXCEPTION,	/* Exception occurred */
		WHY_RERAISE,	/* Exception re-raised by 'finally' */
		WHY_RETURN,	/* 'return' statement */
		WHY_BREAK	/* 'break' statement */
};


/* Interpreter main loop */

object *
eval_code(co, globals, locals, arg)
	codeobject *co;
	object *globals;
	object *locals;
	object *arg;
{
	register unsigned char *next_instr;
	register int opcode;	/* Current opcode */
	register int oparg;	/* Current opcode argument, if any */
	register object **stack_pointer;
	register enum why_code why; /* Reason for block stack unwind */
	register int err;	/* Error status -- nonzero if error */
	register object *x;	/* Result object -- NULL if error */
	register object *v;	/* Temporary objects popped off stack */
	register object *w;
	register object *u;
	register object *t;
	register frameobject *f; /* Current frame */
	object *trace = NULL;	/* Trace function or NULL */
	object *retval;		/* Return value iff why == WHY_RETURN */
	char *name;		/* Name used by some instructions */
#ifdef LLTRACE
	int lltrace = dictlookup(globals, "__lltrace__") != NULL;
#endif
#ifdef DEBUG
	/* Make it easier to find out where we are with dbx */
	char *filename = getstringvalue(co->co_filename);
#endif

/* Code access macros */

#define GETCONST(i)	Getconst(f, i)
#define GETNAME(i)	Getname(f, i)
#define GETNAMEV(i)	Getnamev(f, i)
#define FIRST_INSTR()	(GETUSTRINGVALUE(f->f_code->co_code))
#define INSTR_OFFSET()	(next_instr - FIRST_INSTR())
#define NEXTOP()	(*next_instr++)
#define NEXTARG()	(next_instr += 2, (next_instr[-1]<<8) + next_instr[-2])
#define JUMPTO(x)	(next_instr = FIRST_INSTR() + (x))
#define JUMPBY(x)	(next_instr += (x))

/* Stack manipulation macros */

#define STACK_LEVEL()	(stack_pointer - f->f_valuestack)
#define EMPTY()		(STACK_LEVEL() == 0)
#define TOP()		(stack_pointer[-1])
#define BASIC_PUSH(v)	(*stack_pointer++ = (v))
#define BASIC_POP()	(*--stack_pointer)

#define CHECK_STACK(n)	(STACK_LEVEL() + (n) < f->f_nvalues || \
			  (stack_pointer = extend_stack(f, STACK_LEVEL(), n)))

#ifdef LLTRACE
#define PUSH(v)		(BASIC_PUSH(v), lltrace && prtrace(TOP(), "push"))
#define POP()		(lltrace && prtrace(TOP(), "pop"), BASIC_POP())
#else
#define PUSH(v)		BASIC_PUSH(v)
#define POP()		BASIC_POP()
#endif

	f = newframeobject(
			current_frame,		/*back*/
			co,			/*code*/
			globals,		/*globals*/
			locals,			/*locals*/
			50,			/*nvalues*/
			20);			/*nblocks*/
	if (f == NULL)
		return NULL;
	
	current_frame = f;

	if (sys_trace != NULL) {
		/* sys_trace, if defined, is a function that will
		   be called  on *every* entry to a code block.
		   Its return value, if not None, is a function that
		   will be called at the start of each executed line
		   of code.  (Actually, the function must return
		   itself in order to continue tracing.)
		   The trace functions are called with three arguments:
		   a pointer to the current frame, a string indicating
		   why the function is called, and an argument which
		   depends on the situation.  The global trace function
		   (sys.trace) is also called whenever an exception
		   is detected. */
		if (call_trace(&sys_trace, &trace, f, "call", arg)) {
			/* Trace function raised an error */
			current_frame = f->f_back;
			DECREF(f);
			return NULL;
		}
	}

	if (sys_profile != NULL) {
		/* Similar for sys_profile, except it needn't return
		   itself and isn't called for "line" events */
		if (call_trace(&sys_profile, (object**)0, f, "call", arg)) {
			current_frame = f->f_back;
			DECREF(f);
			return NULL;
		}
	}
	
	next_instr = GETUSTRINGVALUE(f->f_code->co_code);
	stack_pointer = f->f_valuestack;
	
	if (arg != NULL) {
		INCREF(arg);
		PUSH(arg);
	}
	
	why = WHY_NOT;
	err = 0;
	x = None;	/* Not a reference, just anything non-NULL */
	
	for (;;) {
		static int ticker;
		
		/* Do periodic things.
		   Doing this every time through the loop would add
		   too much overhead (a function call per instruction).
		   So we do it only every tenth instruction. */
		
		if (--ticker < 0) {
			ticker = 10;
			if (intrcheck()) {
				err_set(KeyboardInterrupt);
				why = WHY_EXCEPTION;
				goto on_error;
			}

#ifdef USE_THREAD
			if (interpreter_lock) {
				/* Give another thread a chance */

				current_frame = NULL;
				release_lock(interpreter_lock);

				/* Other threads may run now */

				acquire_lock(interpreter_lock, 1);
				current_frame = f;
			}
#endif
		}

		/* Extract opcode and argument */

#ifdef DEBUG
		f->f_lasti = INSTR_OFFSET();
#endif
		
		opcode = NEXTOP();
		if (HAS_ARG(opcode))
			oparg = NEXTARG();

#ifdef LLTRACE
		/* Instruction tracing */
		
		if (lltrace) {
			if (HAS_ARG(opcode)) {
				printf("%d: %d, %d\n",
					(int) (INSTR_OFFSET() - 3),
					opcode, oparg);
			}
			else {
				printf("%d: %d\n",
					(int) (INSTR_OFFSET() - 1), opcode);
			}
		}
#endif

		if (!CHECK_STACK(3)) {
			x = NULL;
			break;
		}

		/* Main switch on opcode */
		
		switch (opcode) {
		
		/* BEWARE!
		   It is essential that any operation that fails sets either
		   x to NULL, err to nonzero, or why to anything but WHY_NOT,
		   and that no operation that succeeds does this! */
		
		/* case STOP_CODE: this is an error! */
		
		case POP_TOP:
			v = POP();
			DECREF(v);
			break;
		
		case ROT_TWO:
			v = POP();
			w = POP();
			PUSH(v);
			PUSH(w);
			break;
		
		case ROT_THREE:
			v = POP();
			w = POP();
			x = POP();
			PUSH(v);
			PUSH(x);
			PUSH(w);
			break;
		
		case DUP_TOP:
			v = TOP();
			INCREF(v);
			PUSH(v);
			break;
		
		case UNARY_POSITIVE:
			v = POP();
			x = pos(v);
			DECREF(v);
			PUSH(x);
			break;
		
		case UNARY_NEGATIVE:
			v = POP();
			x = neg(v);
			DECREF(v);
			PUSH(x);
			break;
		
		case UNARY_NOT:
			v = POP();
			x = not(v);
			DECREF(v);
			PUSH(x);
			break;
		
		case UNARY_CONVERT:
			v = POP();
			x = reprobject(v);
			DECREF(v);
			PUSH(x);
			break;
		
		case UNARY_CALL:
			v = POP();
			f->f_lasti = INSTR_OFFSET() - 1; /* For tracing */
			x = call_object(v, (object *)NULL);
			DECREF(v);
			PUSH(x);
			break;
			
		case UNARY_INVERT:
			v = POP();
			x = invert(v);
			DECREF(v);
			PUSH(x);
			break;
		
		case BINARY_MULTIPLY:
			w = POP();
			v = POP();
			x = mul(v, w);
			DECREF(v);
			DECREF(w);
			PUSH(x);
			break;
		
		case BINARY_DIVIDE:
			w = POP();
			v = POP();
			x = divide(v, w);
			DECREF(v);
			DECREF(w);
			PUSH(x);
			break;
		
		case BINARY_MODULO:
			w = POP();
			v = POP();
			x = rem(v, w);
			DECREF(v);
			DECREF(w);
			PUSH(x);
			break;
		
		case BINARY_ADD:
			w = POP();
			v = POP();
			x = add(v, w);
			DECREF(v);
			DECREF(w);
			PUSH(x);
			break;
		
		case BINARY_SUBTRACT:
			w = POP();
			v = POP();
			x = sub(v, w);
			DECREF(v);
			DECREF(w);
			PUSH(x);
			break;
		
		case BINARY_SUBSCR:
			w = POP();
			v = POP();
			x = apply_subscript(v, w);
			DECREF(v);
			DECREF(w);
			PUSH(x);
			break;
		
		case BINARY_CALL:
			w = POP();
			v = POP();
			f->f_lasti = INSTR_OFFSET() - 1; /* For tracing */
			x = call_object(v, w);
			DECREF(v);
			DECREF(w);
			PUSH(x);
			break;
		
		case BINARY_LSHIFT:
			w = POP();
			v = POP();
			x = lshift(v, w);
			DECREF(v);
			DECREF(w);
			PUSH(x);
			break;
		
		case BINARY_RSHIFT:
			w = POP();
			v = POP();
			x = rshift(v, w);
			DECREF(v);
			DECREF(w);
			PUSH(x);
			break;
		
		case BINARY_AND:
			w = POP();
			v = POP();
			x = and(v, w);
			DECREF(v);
			DECREF(w);
			PUSH(x);
			break;
		
		case BINARY_XOR:
			w = POP();
			v = POP();
			x = xor(v, w);
			DECREF(v);
			DECREF(w);
			PUSH(x);
			break;
		
		case BINARY_OR:
			w = POP();
			v = POP();
			x = or(v, w);
			DECREF(v);
			DECREF(w);
			PUSH(x);
			break;
		
		case SLICE+0:
		case SLICE+1:
		case SLICE+2:
		case SLICE+3:
			if ((opcode-SLICE) & 2)
				w = POP();
			else
				w = NULL;
			if ((opcode-SLICE) & 1)
				v = POP();
			else
				v = NULL;
			u = POP();
			x = apply_slice(u, v, w);
			DECREF(u);
			XDECREF(v);
			XDECREF(w);
			PUSH(x);
			break;
		
		case STORE_SLICE+0:
		case STORE_SLICE+1:
		case STORE_SLICE+2:
		case STORE_SLICE+3:
			if ((opcode-STORE_SLICE) & 2)
				w = POP();
			else
				w = NULL;
			if ((opcode-STORE_SLICE) & 1)
				v = POP();
			else
				v = NULL;
			u = POP();
			t = POP();
			err = assign_slice(u, v, w, t); /* u[v:w] = t */
			DECREF(t);
			DECREF(u);
			XDECREF(v);
			XDECREF(w);
			break;
		
		case DELETE_SLICE+0:
		case DELETE_SLICE+1:
		case DELETE_SLICE+2:
		case DELETE_SLICE+3:
			if ((opcode-DELETE_SLICE) & 2)
				w = POP();
			else
				w = NULL;
			if ((opcode-DELETE_SLICE) & 1)
				v = POP();
			else
				v = NULL;
			u = POP();
			err = assign_slice(u, v, w, (object *)NULL);
							/* del u[v:w] */
			DECREF(u);
			XDECREF(v);
			XDECREF(w);
			break;
		
		case STORE_SUBSCR:
			w = POP();
			v = POP();
			u = POP();
			/* v[w] = u */
			err = assign_subscript(v, w, u);
			DECREF(u);
			DECREF(v);
			DECREF(w);
			break;
		
		case DELETE_SUBSCR:
			w = POP();
			v = POP();
			/* del v[w] */
			err = assign_subscript(v, w, (object *)NULL);
			DECREF(v);
			DECREF(w);
			break;
		
		case PRINT_EXPR:
			v = POP();
			/* Print value except if procedure result */
			if (v != None) {
				flushline();
				x = sysget("stdout");
				softspace(x, 1);
				err = writeobject(v, x, 0);
				flushline();
			}
			DECREF(v);
			break;
		
		case PRINT_ITEM:
			v = POP();
			w = sysget("stdout");
			if (softspace(w, 1))
				writestring(" ", w);
			if (is_stringobject(v)) {
				char *s = getstringvalue(v);
				int len = getstringsize(v);
				err = writeobject(v, w, PRINT_RAW);
				if (err == 0 && len > 0 && s[len-1] == '\n')
					softspace(w, 0);
			}
			else {
				err = writeobject(v, w, 0);
			}
			DECREF(v);
			break;
		
		case PRINT_NEWLINE:
			x = sysget("stdout");
			if (x == NULL)
				err_setstr(RuntimeError, "lost sys.stdout");
			else {
				writestring("\n", x);
				softspace(x, 0);
			}
			break;
		
		case BREAK_LOOP:
			why = WHY_BREAK;
			break;
		
		case RAISE_EXCEPTION:
			v = POP();
			w = POP();
			/* A tuple is equivalent to its first element here */
			while (is_tupleobject(w)) {
				u = w;
				w = gettupleitem(u, 0);
				DECREF(u);
			}
			if (!is_stringobject(w))
				err_setstr(TypeError,
					"exceptions must be strings");
			else
				err_setval(w, v);
			DECREF(v);
			DECREF(w);
			why = WHY_EXCEPTION;
			break;
		
		case LOAD_LOCALS:
			v = f->f_locals;
			INCREF(v);
			PUSH(v);
			break;
		
		case RETURN_VALUE:
			retval = POP();
			why = WHY_RETURN;
			break;
		
		case BUILD_FUNCTION:
			v = POP();
			x = newfuncobject(v, f->f_globals);
			DECREF(v);
			PUSH(x);
			break;
		
		case POP_BLOCK:
			{
				block *b = pop_block(f);
				while (STACK_LEVEL() > b->b_level) {
					v = POP();
					DECREF(v);
				}
			}
			break;
		
		case END_FINALLY:
			v = POP();
			if (is_intobject(v)) {
				why = (enum why_code) getintvalue(v);
				if (why == WHY_RETURN)
					retval = POP();
			}
			else if (is_stringobject(v)) {
				w = POP();
				err_setval(v, w);
				DECREF(w);
				w = POP();
				tb_store(w);
				DECREF(w);
				why = WHY_RERAISE;
			}
			else if (v != None) {
				err_setstr(SystemError,
					"'finally' pops bad exception");
				why = WHY_EXCEPTION;
			}
			DECREF(v);
			break;
		
		case BUILD_CLASS:
			w = POP();
			v = POP();
			x = build_class(v, w);
			PUSH(x);
			DECREF(v);
			DECREF(w);
			break;
		
		case STORE_NAME:
			w = GETNAMEV(oparg);
			v = POP();
			err = dict2insert(f->f_locals, w, v);
			DECREF(v);
			break;
		
		case DELETE_NAME:
			w = GETNAMEV(oparg);
			if ((err = dict2remove(f->f_locals, w)) != 0)
				err_setstr(NameError, getstringvalue(w));
			break;

#ifdef CASE_TOO_BIG
		default: switch (opcode) {
#endif
		
		case UNPACK_VARARG:
			if (EMPTY()) {
				err_setstr(TypeError,
					   "no argument list");
				why = WHY_EXCEPTION;
				break;
			}
			v = POP();
			if (!is_tupleobject(v)) {
				err_setstr(TypeError,
					   "bad argument list");
				why = WHY_EXCEPTION;
			}
			else if (gettuplesize(v) < oparg) {
				err_setstr(TypeError,
					"not enough arguments");
				why = WHY_EXCEPTION;
			}
			else if (oparg == 0) {
				PUSH(v);
				break;
			}
			else {
				x = gettupleslice(v, oparg, gettuplesize(v));
				if (x != NULL) {
					PUSH(x);
					if (!CHECK_STACK(oparg)) {
						x = NULL;
						break;
					}
					for (; --oparg >= 0; ) {
						w = gettupleitem(v, oparg);
						INCREF(w);
						PUSH(w);
					}
				}
			}
			DECREF(v);
			break;
		
		case UNPACK_ARG:
			/* Implement various compatibility hacks:
			   (a) f(a,b,...) should accept f((1,2,...))
			   (b) f((a,b,...)) should accept f(1,2,...)
			   (c) f(self,(a,b,...)) should accept f(x,1,2,...)
			   Actually, (c) is dangerous, and (b) seems
			   unnecessary, but (a) can't be missed...
			*/
			{
				int n;
				if (EMPTY()) {
					err_setstr(TypeError,
						   "no argument list");
					why = WHY_EXCEPTION;
					break;
				}
				v = POP();
				if (!is_tupleobject(v)) {
					err_setstr(TypeError,
						   "bad argument list");
					why = WHY_EXCEPTION;
					break;
				}
				n = gettuplesize(v);
				if (n == 1 && oparg != 1) {
					/* Rule (a) */
					w = gettupleitem(v, 0);
					if (is_tupleobject(w)) {
						INCREF(w);
						DECREF(v);
						v = w;
						n = gettuplesize(v);
					}
				}
#if 0 /* Compatibility hacks no longer needed (I think) */
				else if (n != 1 && oparg == 1) {
					/* Rule (b) */
					PUSH(v);
					break;
					/* Don't fall through */
				}
				else if (n > 2 && oparg == 2) {
					/* Rule (c) */
					int i;
					w = newtupleobject(n-1);
					u = newtupleobject(2);
					if (u == NULL || w == NULL) {
						XDECREF(w);
						XDECREF(u);
						DECREF(v);
						why = WHY_EXCEPTION;
						break;
					}
					t = gettupleitem(v, 0);
					INCREF(t);
					settupleitem(u, 0, t);
					for (i = 1; i < n; i++) {
						t = gettupleitem(v, i);
						INCREF(t);
						settupleitem(w, i-1, t);
					}
					settupleitem(u, 1, w);
					DECREF(v);
					v = u;
					n = 2;
				}
#endif /* Disabled compatibility hacks */
				if (n != oparg) {
					err_setstr(TypeError,
						"arg count mismatch");
					why = WHY_EXCEPTION;
					DECREF(v);
					break;
				}
				PUSH(v);
			}
			/* Fall through */
		case UNPACK_TUPLE:
			v = POP();
			if (!is_tupleobject(v)) {
				err_setstr(TypeError, "unpack non-tuple");
				why = WHY_EXCEPTION;
			}
			else if (gettuplesize(v) != oparg) {
				err_setstr(ValueError,
					"unpack tuple of wrong size");
				why = WHY_EXCEPTION;
			}
			else {
				if (!CHECK_STACK(oparg)) {
					x = NULL;
					break;
				}
				for (; --oparg >= 0; ) {
					w = gettupleitem(v, oparg);
					INCREF(w);
					PUSH(w);
				}
			}
			DECREF(v);
			break;
		
		case UNPACK_LIST:
			v = POP();
			if (!is_listobject(v)) {
				err_setstr(TypeError, "unpack non-list");
				why = WHY_EXCEPTION;
			}
			else if (getlistsize(v) != oparg) {
				err_setstr(ValueError,
					"unpack list of wrong size");
				why = WHY_EXCEPTION;
			}
			else {
				if (!CHECK_STACK(oparg)) {
					x = NULL;
					break;
				}
				for (; --oparg >= 0; ) {
					w = getlistitem(v, oparg);
					INCREF(w);
					PUSH(w);
				}
			}
			DECREF(v);
			break;
		
		case STORE_ATTR:
			name = GETNAME(oparg);
			v = POP();
			u = POP();
			err = setattr(v, name, u); /* v.name = u */
			DECREF(v);
			DECREF(u);
			break;
		
		case DELETE_ATTR:
			name = GETNAME(oparg);
			v = POP();
			err = setattr(v, name, (object *)NULL);
							/* del v.name */
			DECREF(v);
			break;
		
		case STORE_GLOBAL:
			w = GETNAMEV(oparg);
			v = POP();
			err = dict2insert(f->f_globals, w, v);
			DECREF(v);
			break;
		
		case DELETE_GLOBAL:
			w = GETNAMEV(oparg);
			if ((err = dict2remove(f->f_globals, w)) != 0)
				err_setstr(NameError, getstringvalue(w));
			break;
		
		case LOAD_CONST:
			x = GETCONST(oparg);
			INCREF(x);
			PUSH(x);
			break;
		
		case LOAD_NAME:
			w = GETNAMEV(oparg);
			x = dict2lookup(f->f_locals, w);
			if (x == NULL) {
				err_clear();
				x = dict2lookup(f->f_globals, w);
				if (x == NULL) {
					err_clear();
					x = getbuiltin(w);
					if (x == NULL) {
						err_setstr(NameError,
							getstringvalue(w));
						break;
					}
				}
			}
			INCREF(x);
			PUSH(x);
			break;
		
		case LOAD_GLOBAL:
			w = GETNAMEV(oparg);
			x = dict2lookup(f->f_globals, w);
			if (x == NULL) {
				err_clear();
				x = getbuiltin(w);
				if (x == NULL) {
					err_setstr(NameError,
						getstringvalue(w));
					break;
				}
			}
			INCREF(x);
			PUSH(x);
			break;
		
		case LOAD_LOCAL:
			w = GETNAMEV(oparg);
			x = dict2lookup(f->f_locals, w);
			if (x == NULL) {
				err_setstr(NameError, getstringvalue(w));
				break;
			}
			INCREF(x);
			PUSH(x);
			break;
		
		case BUILD_TUPLE:
			x = newtupleobject(oparg);
			if (x != NULL) {
				for (; --oparg >= 0;) {
					w = POP();
					err = settupleitem(x, oparg, w);
					if (err != 0)
						break;
				}
				PUSH(x);
			}
			break;
		
		case BUILD_LIST:
			x =  newlistobject(oparg);
			if (x != NULL) {
				for (; --oparg >= 0;) {
					w = POP();
					err = setlistitem(x, oparg, w);
					if (err != 0)
						break;
				}
				PUSH(x);
			}
			break;
		
		case BUILD_MAP:
			x = newdictobject();
			PUSH(x);
			break;
		
		case LOAD_ATTR:
			name = GETNAME(oparg);
			v = POP();
			x = getattr(v, name);
			DECREF(v);
			PUSH(x);
			break;
		
		case COMPARE_OP:
			w = POP();
			v = POP();
			x = cmp_outcome(oparg, v, w);
			DECREF(v);
			DECREF(w);
			PUSH(x);
			break;
		
		case IMPORT_NAME:
			name = GETNAME(oparg);
			x = import_module(name);
			XINCREF(x);
			PUSH(x);
			break;
		
		case IMPORT_FROM:
			w = GETNAMEV(oparg);
			v = TOP();
			err = import_from(f->f_locals, v, w);
			break;
		
		case JUMP_FORWARD:
			JUMPBY(oparg);
			break;
		
		case JUMP_IF_FALSE:
			err = testbool(TOP());
			if (err > 0)
				err = 0;
			else if (err == 0)
				JUMPBY(oparg);
			break;
		
		case JUMP_IF_TRUE:
			err = testbool(TOP());
			if (err > 0) {
				err = 0;
				JUMPBY(oparg);
			}
			break;
		
		case JUMP_ABSOLUTE:
			JUMPTO(oparg);
			break;
		
		case FOR_LOOP:
			/* for v in s: ...
			   On entry: stack contains s, i.
			   On exit: stack contains s, i+1, s[i];
			   but if loop exhausted:
			   	s, i are popped, and we jump */
			w = POP(); /* Loop index */
			v = POP(); /* Sequence object */
			u = loop_subscript(v, w);
			if (u != NULL) {
				PUSH(v);
				x = newintobject(getintvalue(w)+1);
				PUSH(x);
				DECREF(w);
				PUSH(u);
			}
			else {
				DECREF(v);
				DECREF(w);
				/* A NULL can mean "s exhausted"
				   but also an error: */
				if (err_occurred())
					why = WHY_EXCEPTION;
				else
					JUMPBY(oparg);
			}
			break;
		
		case SETUP_LOOP:
		case SETUP_EXCEPT:
		case SETUP_FINALLY:
			setup_block(f, opcode, INSTR_OFFSET() + oparg,
						STACK_LEVEL());
			break;
		
		case SET_LINENO:
#ifdef LLTRACE
			if (lltrace)
				printf("--- Line %d ---\n", oparg);
#endif
			f->f_lineno = oparg;
			if (trace != NULL) {
				/* Trace each line of code reached */
				f->f_lasti = INSTR_OFFSET();
				err = call_trace(&trace, &trace,
						 f, "line", None);
			}
			break;
		
		default:
			fprintf(stderr,
				"XXX lineno: %d, opcode: %d\n",
				f->f_lineno, opcode);
			err_setstr(SystemError, "eval_code: unknown opcode");
			why = WHY_EXCEPTION;
			break;

#ifdef CASE_TOO_BIG
		}
#endif

		} /* switch */

	    on_error:
		
		/* Quickly continue if no error occurred */
		
		if (why == WHY_NOT) {
			if (err == 0 && x != NULL)
				continue; /* Normal, fast path */
			why = WHY_EXCEPTION;
			x = None;
			err = 0;
		}

#ifdef CHECKEXC
		/* Double-check exception status */
		
		if (why == WHY_EXCEPTION || why == WHY_RERAISE) {
			if (!err_occurred()) {
				fprintf(stderr, "XXX ghost error\n");
				err_setstr(SystemError, "ghost error");
				why = WHY_EXCEPTION;
			}
		}
		else {
			if (err_occurred()) {
				fprintf(stderr, "XXX undetected error\n");
				abort();
				/* NOTREACHED */
				why = WHY_EXCEPTION;
			}
		}
#endif

		/* 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;
			tb_here(f);

			if (trace)
				call_exc_trace(&trace, &trace, f);
			if (sys_profile)
				call_exc_trace(&sys_profile, (object**)0, f);
		}
		
		/* For the rest, treat WHY_RERAISE as WHY_EXCEPTION */
		
		if (why == WHY_RERAISE)
			why = WHY_EXCEPTION;

		/* Unwind stacks if a (pseudo) exception occurred */
		
		while (why != WHY_NOT && f->f_iblock > 0) {
			block *b = pop_block(f);
			while (STACK_LEVEL() > b->b_level) {
				v = POP();
				XDECREF(v);
			}
			if (b->b_type == SETUP_LOOP && why == WHY_BREAK) {
				why = WHY_NOT;
				JUMPTO(b->b_handler);
				break;
			}
			if (b->b_type == SETUP_FINALLY ||
					b->b_type == SETUP_EXCEPT &&
					why == WHY_EXCEPTION) {
				if (why == WHY_EXCEPTION) {
					object *exc, *val;
					err_get(&exc, &val);
					if (val == NULL) {
						val = None;
						INCREF(val);
					}
					v = tb_fetch();
					/* Make the raw exception data
					   available to the handler,
					   so a program can emulate the
					   Python main loop.  Don't do
					   this for 'finally'. */
					if (b->b_type == SETUP_EXCEPT) {
						sysset("exc_traceback", v);
						sysset("exc_value", val);
						sysset("exc_type", exc);
					}
					PUSH(v);
					PUSH(val);
					PUSH(exc);
				}
				else {
					if (why == WHY_RETURN)
						PUSH(retval);
					v = newintobject((long)why);
					PUSH(v);
				}
				why = WHY_NOT;
				JUMPTO(b->b_handler);
				break;
			}
		} /* unwind stack */

		/* End the loop if we still have an error (or return) */
		
		if (why != WHY_NOT)
			break;
		
	} /* main loop */
	
	/* Pop remaining stack entries */
	
	while (!EMPTY()) {
		v = POP();
		XDECREF(v);
	}
	
	if (why != WHY_RETURN)
		retval = NULL;
	
	if (trace) {
		if (why == WHY_RETURN) {
			if (call_trace(&trace, &trace, f, "return", retval)) {
				XDECREF(retval);
				retval = NULL;
				why = WHY_EXCEPTION;
			}
		}
		XDECREF(trace);
	}
	
	if (sys_profile && why == WHY_RETURN) {
		if (call_trace(&sys_profile, (object**)0,
			       f, "return", retval)) {
			XDECREF(retval);
			retval = NULL;
			why = WHY_EXCEPTION;
		}
	}
	
	/* Restore previous frame and release the current one */
	
	current_frame = f->f_back;
	DECREF(f);
	
	return retval;
}

#ifdef LLTRACE
static int
prtrace(v, str)
	object *v;
	char *str;
{
	printf("%s ", str);
	if (printobject(v, stdout, 0) != 0)
		err_clear(); /* Don't know what else to do */
	printf("\n");
}
#endif

static void
call_exc_trace(p_trace, p_newtrace, f)
	object **p_trace, **p_newtrace;
	frameobject *f;
{
	object *type, *value, *traceback, *arg;
	int err;
	err_get(&type, &value);
	if (value == NULL) {
		value = None;
		INCREF(value);
	}
	traceback = tb_fetch();
	arg = newtupleobject(3);
	if (arg == NULL)
		goto cleanup;
	settupleitem(arg, 0, type);
	settupleitem(arg, 1, value);
	settupleitem(arg, 2, traceback);
	err = call_trace(p_trace, p_newtrace, f, "exception", arg);
	if (!err) {
 cleanup:
		/* Restore original exception */
		err_setval(type, value);
		tb_store(traceback);
	}
	XDECREF(arg);
}

static int
call_trace(p_trace, p_newtrace, f, msg, arg)
	object **p_trace; /* in/out; may not be NULL;
			     may not point to NULL variable initially */
	object **p_newtrace; /* in/out; may be NULL;
				may point to NULL variable;
				may be same variable as p_newtrace */
	frameobject *f;
	char *msg;
	object *arg;
{
	object *arglist, *what;
	object *res = NULL;
	static int tracing = 0;
	
	if (tracing) {
		/* Don't do recursive traces */
		if (p_newtrace) {
			XDECREF(*p_newtrace);
			*p_newtrace = NULL;
		}
		return 0;
	}
	
	arglist = newtupleobject(3);
	if (arglist == NULL)
		goto cleanup;
	what = newstringobject(msg);
	if (what == NULL)
		goto cleanup;
	INCREF(f);
	settupleitem(arglist, 0, (object *)f);
	settupleitem(arglist, 1, what);
	if (arg == NULL)
		arg = None;
	INCREF(arg);
	settupleitem(arglist, 2, arg);
	tracing++;
	res = call_object(*p_trace, arglist);
	tracing--;
 cleanup:
	XDECREF(arglist);
	if (res == NULL) {
		/* The trace proc raised an exception */
		tb_here(f);
		DECREF(*p_trace);
		*p_trace = NULL;
		if (p_newtrace) {
			XDECREF(*p_newtrace);
			*p_newtrace = NULL;
		}
		return -1;
	}
	else {
		if (p_newtrace) {
			XDECREF(*p_newtrace);
			if (res == None)
				*p_newtrace = NULL;
			else {
				INCREF(res);
				*p_newtrace = res;
			}
		}
		DECREF(res);
		return 0;
	}
}

object *
getlocals()
{
	if (current_frame == NULL)
		return NULL;
	else
		return current_frame->f_locals;
}

object *
getglobals()
{
	if (current_frame == NULL)
		return NULL;
	else
		return current_frame->f_globals;
}

void
printtraceback(f)
	object *f;
{
	object *v = tb_fetch();
	if (v != NULL) {
		writestring("Stack backtrace (innermost last):\n", f);
		tb_print(v, f);
		DECREF(v);
	}
}


void
flushline()
{
	object *f = sysget("stdout");
	if (softspace(f, 0))
		writestring("\n", f);
}


/* Test a value used as condition, e.g., in a for or if statement.
   Return -1 if an error occurred */

static int
testbool(v)
	object *v;
{
	int res;
	if (v == None)
		res = 0;
	else if (v->ob_type->tp_as_number != NULL)
		res = (*v->ob_type->tp_as_number->nb_nonzero)(v);
	else if (v->ob_type->tp_as_mapping != NULL)
		res = (*v->ob_type->tp_as_mapping->mp_length)(v);
	else if (v->ob_type->tp_as_sequence != NULL)
		res = (*v->ob_type->tp_as_sequence->sq_length)(v);
	else
		res = 1;
	if (res > 0)
		res = 1;
	return res;
}

static object *
or(v, w)
	object *v, *w;
{
	if (v->ob_type->tp_as_number != NULL) {
		object *x;
		object * (*f) FPROTO((object *, object *));
		if (coerce(&v, &w) != 0)
			return NULL;
		if ((f = v->ob_type->tp_as_number->nb_or) != NULL)
			x = (*f)(v, w);
		DECREF(v);
		DECREF(w);
		if (f != NULL)
			return x;
	}
	err_setstr(TypeError, "bad operand type(s) for |");
	return NULL;
}

static object *
xor(v, w)
	object *v, *w;
{
	if (v->ob_type->tp_as_number != NULL) {
		object *x;
		object * (*f) FPROTO((object *, object *));
		if (coerce(&v, &w) != 0)
			return NULL;
		if ((f = v->ob_type->tp_as_number->nb_xor) != NULL)
			x = (*f)(v, w);
		DECREF(v);
		DECREF(w);
		if (f != NULL)
			return x;
	}
	err_setstr(TypeError, "bad operand type(s) for ^");
	return NULL;
}

static object *
and(v, w)
	object *v, *w;
{
	if (v->ob_type->tp_as_number != NULL) {
		object *x;
		object * (*f) FPROTO((object *, object *));
		if (coerce(&v, &w) != 0)
			return NULL;
		if ((f = v->ob_type->tp_as_number->nb_and) != NULL)
			x = (*f)(v, w);
		DECREF(v);
		DECREF(w);
		if (f != NULL)
			return x;
	}
	err_setstr(TypeError, "bad operand type(s) for &");
	return NULL;
}

static object *
lshift(v, w)
	object *v, *w;
{
	if (v->ob_type->tp_as_number != NULL) {
		object *x;
		object * (*f) FPROTO((object *, object *));
		if (coerce(&v, &w) != 0)
			return NULL;
		if ((f = v->ob_type->tp_as_number->nb_lshift) != NULL)
			x = (*f)(v, w);
		DECREF(v);
		DECREF(w);
		if (f != NULL)
			return x;
	}
	err_setstr(TypeError, "bad operand type(s) for <<");
	return NULL;
}

static object *
rshift(v, w)
	object *v, *w;
{
	if (v->ob_type->tp_as_number != NULL) {
		object *x;
		object * (*f) FPROTO((object *, object *));
		if (coerce(&v, &w) != 0)
			return NULL;
		if ((f = v->ob_type->tp_as_number->nb_rshift) != NULL)
			x = (*f)(v, w);
		DECREF(v);
		DECREF(w);
		if (f != NULL)
			return x;
	}
	err_setstr(TypeError, "bad operand type(s) for >>");
	return NULL;
}

static object *
add(v, w)
	object *v, *w;
{
	if (v->ob_type->tp_as_sequence != NULL)
		return (*v->ob_type->tp_as_sequence->sq_concat)(v, w);
	else if (v->ob_type->tp_as_number != NULL) {
		object *x;
		if (coerce(&v, &w) != 0)
			return NULL;
		x = (*v->ob_type->tp_as_number->nb_add)(v, w);
		DECREF(v);
		DECREF(w);
		return x;
	}
	else {
		err_setstr(TypeError, "+ not supported by operands");
		return NULL;
	}
}

static object *
sub(v, w)
	object *v, *w;
{
	if (v->ob_type->tp_as_number != NULL) {
		object *x;
		if (coerce(&v, &w) != 0)
			return NULL;
		x = (*v->ob_type->tp_as_number->nb_subtract)(v, w);
		DECREF(v);
		DECREF(w);
		return x;
	}
	err_setstr(TypeError, "bad operand type(s) for -");
	return NULL;
}

static object *
mul(v, w)
	object *v, *w;
{
	typeobject *tp;
	tp = v->ob_type;
	if (tp->tp_as_number != NULL &&
	    w->ob_type->tp_as_sequence != NULL &&
	    !is_instanceobject(v)) {
		/* number*sequence -- swap v and w */
		object *tmp = v;
		v = w;
		w = tmp;
		tp = v->ob_type;
	}
	if (tp->tp_as_number != NULL) {
		object *x;
		if (is_instanceobject(v)) {
			/* Instances of user-defined classes get their
			   other argument uncoerced, so they may
			   implement sequence*number as well as
			   number*number. */
			INCREF(v);
			INCREF(w);
		}
		else if (coerce(&v, &w) != 0)
			return NULL;
		x = (*v->ob_type->tp_as_number->nb_multiply)(v, w);
		DECREF(v);
		DECREF(w);
		return x;
	}
	if (tp->tp_as_sequence != NULL) {
		if (!is_intobject(w)) {
			err_setstr(TypeError,
				"can't multiply sequence with non-int");
			return NULL;
		}
		return (*tp->tp_as_sequence->sq_repeat)
						(v, (int)getintvalue(w));
	}
	err_setstr(TypeError, "bad operand type(s) for *");
	return NULL;
}

static object *
divide(v, w)
	object *v, *w;
{
	if (v->ob_type->tp_as_number != NULL) {
		object *x;
		if (coerce(&v, &w) != 0)
			return NULL;
		x = (*v->ob_type->tp_as_number->nb_divide)(v, w);
		DECREF(v);
		DECREF(w);
		return x;
	}
	err_setstr(TypeError, "bad operand type(s) for /");
	return NULL;
}

static object *
rem(v, w)
	object *v, *w;
{
	if (v->ob_type->tp_as_number != NULL) {
		object *x;
		if (coerce(&v, &w) != 0)
			return NULL;
		x = (*v->ob_type->tp_as_number->nb_remainder)(v, w);
		DECREF(v);
		DECREF(w);
		return x;
	}
	err_setstr(TypeError, "bad operand type(s) for %");
	return NULL;
}

static object *
neg(v)
	object *v;
{
	if (v->ob_type->tp_as_number != NULL)
		return (*v->ob_type->tp_as_number->nb_negative)(v);
	err_setstr(TypeError, "bad operand type(s) for unary -");
	return NULL;
}

static object *
pos(v)
	object *v;
{
	if (v->ob_type->tp_as_number != NULL)
		return (*v->ob_type->tp_as_number->nb_positive)(v);
	err_setstr(TypeError, "bad operand type(s) for unary +");
	return NULL;
}

static object *
invert(v)
	object *v;
{
	object * (*f) FPROTO((object *));
	if (v->ob_type->tp_as_number != NULL &&
		(f = v->ob_type->tp_as_number->nb_invert) != NULL)
		return (*f)(v);
	err_setstr(TypeError, "bad operand type(s) for unary ~");
	return NULL;
}

static object *
not(v)
	object *v;
{
	int outcome = testbool(v);
	object *w;
	if (outcome < 0)
		return NULL;
	if (outcome == 0)
		w = True;
	else
		w = False;
	INCREF(w);
	return w;
}
/* External interface to call any callable object. The arg may be NULL. */

object *
call_object(func, arg)
	object *func;
	object *arg;
{
	if (is_instancemethodobject(func) || is_funcobject(func))
		return call_function(func, arg);
	else
		return call_builtin(func, arg);
}

static object *
call_builtin(func, arg)
	object *func;
	object *arg;
{
	if (is_methodobject(func)) {
		method meth = getmethod(func);
		object *self = getself(func);
		if (!getvarargs(func) && arg != NULL && is_tupleobject(arg)) {
			int size = gettuplesize(arg);
			if (size == 1)
				arg = gettupleitem(arg, 0);
			else if (size == 0)
				arg = NULL;
		}
		return (*meth)(self, arg);
	}
	if (is_classobject(func)) {
		if (arg != NULL &&
				!(is_tupleobject(arg) &&
					gettuplesize(arg) == 0)) {
			err_setstr(TypeError,
				"classobject() allows no arguments");
			return NULL;
		}
		return newinstanceobject(func);
	}
	err_setstr(TypeError, "call of non-function");
	return NULL;
}

static object *
call_function(func, arg)
	object *func;
	object *arg;
{
	object *newarg = NULL;
	object *newlocals, *newglobals;
	object *co, *v;
	
	if (is_instancemethodobject(func)) {
		int argcount;
		object *self = instancemethodgetself(func);
		func = instancemethodgetfunc(func);
		if (arg == NULL)
			argcount = 0;
		else if (is_tupleobject(arg))
			argcount = gettuplesize(arg);
		else
			argcount = 1;
		newarg = newtupleobject(argcount + 1);
		if (newarg == NULL)
			return NULL;
		INCREF(self);
		settupleitem(newarg, 0, self);
		if (arg != NULL && !is_tupleobject(arg)) {
			INCREF(arg);
			settupleitem(newarg, 1, arg);
		}
		else {
			int i;
			object *v;
			for (i = 0; i < argcount; i++) {
				v = gettupleitem(arg, i);
				XINCREF(v);
				settupleitem(newarg, i+1, v);
			}
		}
		arg = newarg;
	}
	else {
		if (!is_funcobject(func)) {
			err_setstr(TypeError, "call of non-function");
			return NULL;
		}
	}
	
	co = getfunccode(func);
	if (co == NULL) {
		XDECREF(newarg);
		return NULL;
	}
	if (!is_codeobject(co)) {
		fprintf(stderr, "XXX Bad code\n");
		abort();
	}
	newlocals = newdictobject();
	if (newlocals == NULL) {
		XDECREF(newarg);
		return NULL;
	}
	
	newglobals = getfuncglobals(func);
	INCREF(newglobals);
	
	v = eval_code((codeobject *)co, newglobals, newlocals, arg);
	
	DECREF(newlocals);
	DECREF(newglobals);
	
	XDECREF(newarg);
	
	return v;
}

static object *
apply_subscript(v, w)
	object *v, *w;
{
	typeobject *tp = v->ob_type;
	if (tp->tp_as_sequence == NULL && tp->tp_as_mapping == NULL) {
		err_setstr(TypeError, "unsubscriptable object");
		return NULL;
	}
	if (tp->tp_as_mapping != NULL) {
		return (*tp->tp_as_mapping->mp_subscript)(v, w);
	}
	else {
		int i;
		if (!is_intobject(w)) {
			err_setstr(TypeError, "sequence subscript not int");
			return NULL;
		}
		i = getintvalue(w);
		if (i < 0) {
			int len = (*tp->tp_as_sequence->sq_length)(v);
			if (len < 0)
				return NULL;
			i += len;
		}
		return (*tp->tp_as_sequence->sq_item)(v, i);
	}
}

static object *
loop_subscript(v, w)
	object *v, *w;
{
	sequence_methods *sq = v->ob_type->tp_as_sequence;
	int i, n;
	if (sq == NULL) {
		err_setstr(TypeError, "loop over non-sequence");
		return NULL;
	}
	i = getintvalue(w);
	n = (*sq->sq_length)(v);
	if (n < 0)
		return NULL; /* Exception */
	if (i >= n)
		return NULL; /* End of loop */
	return (*sq->sq_item)(v, i);
}

static int
slice_index(v, isize, pi)
	object *v;
	int isize;
	int *pi;
{
	if (v != NULL) {
		if (!is_intobject(v)) {
			err_setstr(TypeError, "slice index must be int");
			return -1;
		}
		*pi = getintvalue(v);
		if (*pi < 0)
			*pi += isize;
	}
	return 0;
}

static object *
apply_slice(u, v, w) /* return u[v:w] */
	object *u, *v, *w;
{
	typeobject *tp = u->ob_type;
	int ilow, ihigh, isize;
	if (tp->tp_as_sequence == NULL) {
		err_setstr(TypeError, "only sequences can be sliced");
		return NULL;
	}
	ilow = 0;
	isize = ihigh = (*tp->tp_as_sequence->sq_length)(u);
	if (isize < 0)
		return NULL;
	if (slice_index(v, isize, &ilow) != 0)
		return NULL;
	if (slice_index(w, isize, &ihigh) != 0)
		return NULL;
	return (*tp->tp_as_sequence->sq_slice)(u, ilow, ihigh);
}

static int
assign_subscript(w, key, v) /* w[key] = v */
	object *w;
	object *key;
	object *v;
{
	typeobject *tp = w->ob_type;
	sequence_methods *sq;
	mapping_methods *mp;
	int (*func)();
	if ((mp = tp->tp_as_mapping) != NULL &&
			(func = mp->mp_ass_subscript) != NULL) {
		return (*func)(w, key, v);
	}
	else if ((sq = tp->tp_as_sequence) != NULL &&
			(func = sq->sq_ass_item) != NULL) {
		if (!is_intobject(key)) {
			err_setstr(TypeError,
			"sequence subscript must be integer (assign or del)");
			return -1;
		}
		else {
			int i = getintvalue(key);
			if (i < 0) {
				int len = (*sq->sq_length)(w);
				if (len < 0)
					return -1;
				i += len;
			}
			return (*func)(w, i, v);
		}
	}
	else {
		err_setstr(TypeError,
				"can't assign to this subscripted object");
		return -1;
	}
}

static int
assign_slice(u, v, w, x) /* u[v:w] = x */
	object *u, *v, *w, *x;
{
	sequence_methods *sq = u->ob_type->tp_as_sequence;
	int ilow, ihigh, isize;
	if (sq == NULL) {
		err_setstr(TypeError, "assign to slice of non-sequence");
		return -1;
	}
	if (sq == NULL || sq->sq_ass_slice == NULL) {
		err_setstr(TypeError, "unassignable slice");
		return -1;
	}
	ilow = 0;
	isize = ihigh = (*sq->sq_length)(u);
	if (isize < 0)
		return -1;
	if (slice_index(v, isize, &ilow) != 0)
		return -1;
	if (slice_index(w, isize, &ihigh) != 0)
		return -1;
	return (*sq->sq_ass_slice)(u, ilow, ihigh, x);
}

static int
cmp_exception(err, v)
	object *err, *v;
{
	if (is_tupleobject(v)) {
		int i, n;
		n = gettuplesize(v);
		for (i = 0; i < n; i++) {
			/* Test recursively */
			if (cmp_exception(err, gettupleitem(v, i)))
				return 1;
		}
		return 0;
	}
	return err == v;
}

static int
cmp_member(v, w)
	object *v, *w;
{
	int i, n, cmp;
	object *x;
	sequence_methods *sq;
	/* Special case for char in string */
	if (is_stringobject(w)) {
		register char *s, *end;
		register char c;
		if (!is_stringobject(v) || getstringsize(v) != 1) {
			err_setstr(TypeError,
			    "string member test needs char left operand");
			return -1;
		}
		c = getstringvalue(v)[0];
		s = getstringvalue(w);
		end = s + getstringsize(w);
		while (s < end) {
			if (c == *s++)
				return 1;
		}
		return 0;
	}
	sq = w->ob_type->tp_as_sequence;
	if (sq == NULL) {
		err_setstr(TypeError,
			"'in' or 'not in' needs sequence right argument");
		return -1;
	}
	n = (*sq->sq_length)(w);
	if (n < 0)
		return -1;
	for (i = 0; i < n; i++) {
		x = (*sq->sq_item)(w, i);
		cmp = cmpobject(v, x);
		XDECREF(x);
		if (cmp == 0)
			return 1;
	}
	return 0;
}

static object *
cmp_outcome(op, v, w)
	int op;
	register object *v;
	register object *w;
{
	register int cmp;
	register int res = 0;
	switch (op) {
	case IS:
	case IS_NOT:
		res = (v == w);
		if (op == (int) IS_NOT)
			res = !res;
		break;
	case IN:
	case NOT_IN:
		res = cmp_member(v, w);
		if (res < 0)
			return NULL;
		if (op == (int) NOT_IN)
			res = !res;
		break;
	case EXC_MATCH:
		res = cmp_exception(v, w);
		break;
	default:
		cmp = cmpobject(v, w);
		switch (op) {
		case LT: res = cmp <  0; break;
		case LE: res = cmp <= 0; break;
		case EQ: res = cmp == 0; break;
		case NE: res = cmp != 0; break;
		case GT: res = cmp >  0; break;
		case GE: res = cmp >= 0; break;
		/* XXX no default? (res is initialized to 0 though) */
		}
	}
	v = res ? True : False;
	INCREF(v);
	return v;
}

static int
import_from(locals, v, name)
	object *locals;
	object *v;
	object *name;
{
	object *w, *x;
	w = getmoduledict(v);
	if (getstringvalue(name)[0] == '*') {
		int i;
		int n = getdictsize(w);
		for (i = 0; i < n; i++) {
			name = getdict2key(w, i);
			if (name == NULL || getstringvalue(name)[0] == '_')
				continue;
			x = dict2lookup(w, name);
			if (x == NULL) {
				/* XXX can't happen? */
				err_setstr(SystemError, getstringvalue(name));
				return -1;
			}
			if (dict2insert(locals, name, x) != 0)
				return -1;
		}
		return 0;
	}
	else {
		x = dict2lookup(w, name);
		if (x == NULL) {
			char buf[250];
			sprintf(buf, "cannot import name %.230s",
				getstringvalue(name));
			err_setstr(ImportError, buf);
			return -1;
		}
		else
			return dict2insert(locals, name, x);
	}
}

static object *
build_class(v, w)
	object *v; /* None or tuple containing base classes */
	object *w; /* dictionary */
{
	if (is_tupleobject(v)) {
		int i;
		for (i = gettuplesize(v); --i >= 0; ) {
			object *x = gettupleitem(v, i);
			if (!is_classobject(x)) {
				err_setstr(TypeError,
					"base is not a class object");
				return NULL;
			}
		}
	}
	else {
		v = NULL;
	}
	if (!is_dictobject(w)) {
		err_setstr(SystemError, "build_class with non-dictionary");
		return NULL;
	}
	return newclassobject(v, w, (object *) NULL);
}