[Python-bugs-list] [ python-Bugs-702775 ] dumbdbm __del__ bug

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Bugs item #702775, was opened at 2003-03-13 15:27
You can respond by visiting: 
https://sourceforge.net/tracker/?func=detail&atid=105470&aid=702775&group_id=5470

Category: Python Library
Group: Python 2.3
Status: Open
Resolution: None
Priority: 5
Submitted By: Jane Austine (janeaustine50)
Assigned to: Nobody/Anonymous (nobody)
Summary: dumbdbm __del__ bug

Initial Comment:
I used shelve.py and it falls back on dumbdbm when no
possible alternatives are found on the system.

I found this error, which is recurrent and deterministic:

Exception exceptions.AttributeError: "'NoneType' object 
has no
attribute 'error'" in <bound method _Database.__del__ of
<dumbdbm._Database instance at 0x820c71c>> ignored

The problem seems to reside in the __del__ of 
dumbdbm._Database:

class _Database:
...
    def __del__(self):
        if self._index is not None:
            self._commit()
...
    def _commit(self):
        try: _os.unlink(self._bakfile)
        except _os.error: pass
        try: _os.rename(self._dirfile, self._bakfile)
        except _os.error: pass
        f = _open(self._dirfile, 'w', self._mode)
        for key, (pos, siz) in self._index.items():
            f.write("%s, (%s, %s)\n" % (`key`, `pos`, `siz`))
        f.close()

My investigation showed that the error was from 
_commit. When
it was called, _os or _open was both None. And the 
exception
catch didn't work quite safely cause its in the "except" 
clause.

The reason I suspect is when the time that 
_Database.__del__ was
called the os module(which is imported as _os) is 
already removed out.

I changed the code as:

    def _commit(self):
        global _os
        if _os is None:
            import os as _os
            import __builtin__
            _open = __builtin__.open
        try: _os.unlink(self._bakfile)
        except _os.error: pass
        try: _os.rename(self._dirfile, self._bakfile)
        except _os.error: pass
        ......

Now it works without any problems, AFAIK.



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

Comment By: June Kim (juneaftn)
Date: 2003-03-14 02:02

Message:
Logged In: YES 
user_id=116941

see the thread at http://groups.google.com/groups?
selm=ba1e306f.0303111337.72a696c7%
40posting.google.com , esp. by my name.

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You can respond by visiting: 
https://sourceforge.net/tracker/?func=detail&atid=105470&aid=702775&group_id=5470