[Python-bugs-list] [ python-Bugs-757818 ] tuple assignment -- SystemError: unknown opcode

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Bugs item #757818, was opened at 2003-06-20 13:19
Message generated for change (Comment added) made by jackjansen
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https://sourceforge.net/tracker/?func=detail&atid=105470&aid=757818&group_id=5470

Category: Python Interpreter Core
Group: Python 2.3
Status: Open
Resolution: None
Priority: 5
Submitted By: Mark J (average)
Assigned to: Nobody/Anonymous (nobody)
Summary: tuple assignment -- SystemError: unknown opcode

Initial Comment:
Python 2.3b1 (#2, Jun  4 2003, 03:08:06)
[GCC 3.2.2 20030222 (Red Hat Linux 3.2.2-5)] on linux2
>>> i,j = True and (1, -1) or (-1, 1)
XXX lineno: 1, opcode: 0
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
SystemError: unknown opcode
>>> i,j = True and (1, -1)  #works
>>> True and (1, -1) or (-1, 1)  #also works
(1, -1)
>>> i,j = (1, -1) or (-1, 1) #nope
XXX lineno: 1, opcode: 0
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
SystemError: unknown opcode
>>> i,j = False and (1, -1) or (-1, 1) #works
>>> i,j
(-1, 1)

Thanks guys!

Mark

P.S. -1 on keyword initialization of dictionary (Liskov)
P.P.S. +1 on adding keys from iterable

$0.02 (*clink*)

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>Comment By: Jack Jansen (jackjansen)
Date: 2003-06-20 15:01

Message:
Logged In: YES 
user_id=45365

Looks like one of the recent peephole optimizations is to blame, if 
I disassemble a function with i,j = True and (1, -1) or (-1, 1) in it 
I get:
  2           0 LOAD_GLOBAL              0 (True)
              3 JUMP_IF_FALSE           10 (to 16)
              6 POP_TOP             
              7 LOAD_CONST               1 (1)
             10 LOAD_CONST               2 (-1)
             13 BUILD_TUPLE              2
        >>   16 JUMP_IF_TRUE            10 (to 29)
             19 POP_TOP             
             20 LOAD_CONST               2 (-1)
             23 LOAD_CONST               1 (1)
             26 ROT_TWO             
             27 JUMP_FORWARD             2 (to 32)
             30 DUP_TOP             
             31 POP_TOP             
        >>   32 STORE_FAST               0 (i)
             35 STORE_FAST               1 (j)
             38 LOAD_CONST               0 (None)
             41 RETURN_VALUE        

Note the jump at address 16 going to 29, which isn't at an 
instruction boundary. 

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