[Python-bugs-list] [ python-Bugs-563148 ] built-in LIST operation has bug

[noreply@sourceforge.net]

Bugs item #563148, was opened at 2002-06-01 01:23
You can respond by visiting: 
http://sourceforge.net/tracker/?func=detail&atid=105470&aid=563148&group_id=5470

Category: Python Interpreter Core
Group: Python 2.2.1
>Status: Closed
>Resolution: Invalid
Priority: 5
Submitted By: Tom Stanik (mytost)
>Assigned to: Michael Hudson (mwh)
Summary: built-in LIST operation has bug

Initial Comment:
example, to create a list of lists one can enter:

>>> d=[[0] * 4] * 5
>>> print d
[[0, 0, 0, 0], [0, 0, 0, 0], [0, 0, 0, 0], [0, 0, 0, 0], [0, 0, 0, 
0]]

if you want to change the first element in the first list:

>>> d[0][0]=1
>>> print d
[[1, 0, 0, 0], [1, 0, 0, 0], [1, 0, 0, 0], [1, 0, 0, 0], [1, 0, 0, 
0]] ***** INCORECT *****, all the first element changed

Alternatively, if you build the list manually:

>>> d=[0,0,0,0,0]
>>> d[0]=[0,0,0,0]
>>> d[1]=[0,0,0,0]
>>> d[2]=[0,0,0,0]
>>> d[3]=[0,0,0,0]
>>> print d
[[0, 0, 0, 0], [0, 0, 0, 0], [0, 0, 0, 0], [0, 0, 0, 0], [0, 0, 0, 
0]] 

changing the first element in the first list yields the 
correct result

>>> d[0][0]=1
>>> print d
[[1, 0, 0, 0], [0, 0, 0, 0], [0, 0, 0, 0], [0, 0, 0, 0], [0, 0, 0, 
0]] ***** CORRECT *****

The same list depending on hows it built yields a 
different behavior

my version of python:

$ python -v
# /usr/local/lib/python2.2/site.pyc 
matches /usr/local/lib/python2.2/site.py
import site # precompiled 
from /usr/local/lib/python2.2/site.pyc
# /usr/local/lib/python2.2/os.pyc 
matches /usr/local/lib/python2.2/os.py
import os # precompiled 
from /usr/local/lib/python2.2/os.pyc
import posix # builtin
# /usr/local/lib/python2.2/posixpath.pyc 
matches /usr/local/lib/python2.2/posixpath.py
import posixpath # precompiled 
from /usr/local/lib/python2.2/posixpath.pyc
# /usr/local/lib/python2.2/stat.pyc 
matches /usr/local/lib/python2.2/stat.py
import stat # precompiled 
from /usr/local/lib/python2.2/stat.pyc
# /usr/local/lib/python2.2/UserDict.pyc 
matches /usr/local/lib/python2.2/UserDict.py
import UserDict # precompiled 
from /usr/local/lib/python2.2/UserDict.pyc
# /usr/local/lib/python2.2/copy_reg.pyc 
matches /usr/local/lib/python2.2/copy_reg.py
import copy_reg # precompiled 
from /usr/local/lib/python2.2/copy_reg.pyc
# /usr/local/lib/python2.2/types.pyc 
matches /usr/local/lib/python2.2/types.py
import types # precompiled 
from /usr/local/lib/python2.2/types.pyc
# /usr/local/lib/python2.2/__future__.pyc 
matches /usr/local/lib/python2.2/__future__.py
import __future__ # precompiled 
from /usr/local/lib/python2.2/__future__.pyc
Python 2.2.1 (#1, May 10 2002, 23:36:51) 
[GCC 2.95.3 20010315 (release) [FreeBSD]] on freebsd4
Type "help", "copyright", "credits" or "license" for more 
information.
dlopen("/usr/local/lib/python2.2/lib-dynload/readline.so", 
2);
import readline # dynamically loaded 
from /usr/local/lib/python2.2/lib-dynload/readline.so
>>> 




----------------------------------------------------------------------

>Comment By: Michael Hudson (mwh)
Date: 2002-06-01 15:03

Message:
Logged In: YES 
user_id=6656

Sigh.  This is not a bug.  You could try reading 

http://starship.python.net/crew/mwh/hacks/objectthink.html

to gain a better understanding of what's going on.

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You can respond by visiting: 
http://sourceforge.net/tracker/?func=detail&atid=105470&aid=563148&group_id=5470