dumbdbm module broken in Python2.3?

[Jane Austine]

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.

Am I right on the track?

Jane