[Python-bugs-list] [ python-Bugs-478534 ] SystemError with WeakKeyDictionary

Wed, 07 Nov 2001 09:42:28 -0800

Bugs item #478534, was opened at 2001-11-05 19:15
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Category: Python Interpreter Core
Group: Python 2.2
Status: Open
Resolution: Works For Me
Priority: 5
Submitted By: Sverker Nilsson (svenil)
Assigned to: Fred L. Drake, Jr. (fdrake)
Summary: SystemError with WeakKeyDictionary

Initial Comment:
SystemError with WeakKeyDictionary

A SystemError is generated when trying
to iterate over a function returned from a
function that stored it in a WeakKeyDictionary.
The expected error was TypeError.

Sverker Nilsson

Examples:

This program gives a SystemError:

import weakref
ref = weakref.WeakKeyDictionary()

def encapsulate():
    f = lambda : ()
    ref[f] = None
    return f

for x in encapsulate():
 print x

Python 2.2b1 (#5, Oct 20 2001, 03:03:53) 
[GCC 2.95.2 20000220 (Debian GNU/Linux)] on linux2
Type "help", "copyright", "credits" or "license" for
more information.
...
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
  File "/tmp/pythona04442", line 9, in ?
    for x in encapsulate():
SystemError: error return without exception set
>>> 

A variation of it, with a temporary variable,
gives the expected TypeError:

import weakref
ref = weakref.WeakKeyDictionary()

def encapsulate():
    f = lambda : ()
    ref[f] = None
    return f

g = encapsulate()
for x in g:
 print x

Traceback (most recent call last):
  File "<stdin>", line 1, in ?
  File "/tmp/pythona04442", line 10, in ?
    for x in g:
TypeError: iteration over non-sequence
>>>

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>Comment By: Sverker Nilsson (svenil)
Date: 2001-11-07 09:42

Message:
Logged In: YES 
user_id=356603

I have got the cvs version now. It also gives the error or
segmentation fault. Either compiled with Py_Debug enabled in
configuration, or with another version of my test program.
(The Py_Debug definition changes what Python does in
eval_frame so the error is revealed in the original test. )
See attached files: wrbug4.py, new test program.
wrbug4.mail, some info. wrbug4.gdb-transcript, a raw gdb
transcript... /Sverker

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

Comment By: Sverker Nilsson (svenil)
Date: 2001-11-06 11:07

Message:
Logged In: YES 
user_id=356603

Ooops, in the example I sent you I hadnt removed
the self parameter after all. I  mixed up something.
But when I did remove the self parameter it went
as I said. Actually, I get a segmentation fault
running it directly from the shell. (When running
it from Emacs mode or importing it I get SystemError.)

Sverker

Shell transcript:

nicosys [228] python defenvbug3.py
first add ok
Segmentation fault
nicosys [229] cat defenvbug3.py
import weakref
ref = weakref.WeakKeyDictionary()

class MyError(Exception):
    pass

def add(x):
    raise MyError

def encapsulate():
    f = lambda : ()
    ref[f] = None
    return f

try:
    add(encapsulate())
except MyError: pass

print 'first add ok'

add(encapsulate())
# Here we would like to get Exception but gets SystemError
instead.

nicosys [230] python           
Python 2.2b1 (#5, Oct 20 2001, 03:03:53) 
[GCC 2.95.2 20000220 (Debian GNU/Linux)] on linux2
Type "help", "copyright", "credits" or "license" for more
information.
>>> import defenvbug3.py
first add ok
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
SystemError: NULL result without error in PyObject_Call
>>> 
nicosys [231] whence python
/usr/local/bin/python is actually /hda7/local/bin/python
/usr/local/bin/python: ELF 32-bit LSB executable i386 (386
and up) Version 1
nicosys [232] ldd /hda7/local/bin/python
        libdl.so.2 => /lib/libdl.so.2 (0x40018000)
        libpthread.so.0 => /lib/libpthread.so.0 (0x4001d000)
        libutil.so.1 => /lib/libutil.so.1 (0x40030000)
        libm.so.6 => /lib/libm.so.6 (0x40033000)
        libc.so.6 => /lib/libc.so.6 (0x40052000)
        /lib/ld-linux.so.2 => /lib/ld-linux.so.2
(0x40000000)
nicosys [233] 

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

Comment By: Sverker Nilsson (svenil)
Date: 2001-11-06 10:47

Message:
Logged In: YES 
user_id=356603

To answer your question, I am using 2.2b1,
from the tarball not from CVS.

In the second example, I get SystemError
from the first call to add actually. I
thought it was from the second one, but
since I changed from my own exception
class to Exception it became hidden. 

When I remove the uninteded self parameter
of add, I get SystemError in the second
call, as I thought I was getting.

But you get TypeError.. hmmm..

I suppose I should download the CVS then?..
Or maybe wait for 2.2b2..

Sverker

ps. Here's my updated second example, anyway..

import weakref
ref = weakref.WeakKeyDictionary()

class MyError(Exception):
    pass

def add(self, x):
    raise MyError

def encapsulate():
    f = lambda : ()
    ref[f] = None
    return f

try:
    add(encapsulate())
except MyError: pass

print 'first add ok'

add(encapsulate())
# Here we would like to get Exception but gets SystemError
instead.

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

Comment By: Fred L. Drake, Jr. (fdrake)
Date: 2001-11-06 08:33

Message:
Logged In: YES 
user_id=3066

I cannot reproduce this using either code snippet.  Note
that the second example should (and does for me) raise
TypeError when calling add() -- you left in a "self" that
appears to be unintended.

Are you using 2.2b1 or CVS python?

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

Comment By: Sverker Nilsson (svenil)
Date: 2001-11-05 23:17

Message:
Logged In: YES 
user_id=356603

The same problem now occured in another situation. I am
enclosing the condensed program. /Sverker

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

You can respond by visiting: 
http://sourceforge.net/tracker/?func=detail&atid=105470&aid=478534&group_id=5470