[Python] Finding an error name

[Bob Miller]

Martin Kelly wrote:

> I'm trying to figure out what error type is given by shelve.open(file, 
> "r") when the file does not exist.

The exception type is an anydbm.error.  But I don't understand the
source code.

>From anydbm.py:

    # ...
    class error(Exception):
        pass
    # ...
    error = tuple(_errors)
    # ... line 77:
        raise error, "need 'c' or 'n'..."

The Python Reference Manual doesn't say anything about using a tuple
in a raise statement.

    http://docs.python.org/ref/raise.html

But that's what it is.  Here's a sample shell session.

    Python 2.4.3 (#1, Jun 28 2006, 06:34:30) 
    [GCC 3.4.6 (Gentoo 3.4.6-r1, ssp-3.4.5-1.0, pie-8.7.9)] on linux2
    Type "help", "copyright", "credits" or "license" for more information.
    >>> import shelve
    >>> import anydbm
    >>> try:
    ...     shelve.open('nonexistent', 'r')
    ... except anydbm.error:
    ...     print 'caught it'
    ... 
    caught it
    Exception exceptions.AttributeError: "DbfilenameShelf instance has no
    attribute 'writeback'" in  ignored
    >>> anydbm.error
    (<class anydbm.error at 0xb7f48bfc>,
     <class bsddb._db.DBError at 0xb7f5623c>,
     <class gdbm.error at 0xb7f48cbc>,
     <class dbm.error at 0xb7f5b38c>,
     <class exceptions.IOError at 0xb7f774ac>)
    >>> 

So, uh, what's that weird other bit, exceptions.AttributeError?
That's a bug in Python 2.4.3.  You can see in shelve.py that
Shelf.__del__() calls Shelf.close() calls Shelf.sync() which
references self.writeback even though that attribute doesn't exist.
It also references self.dict which also doesn't exist.

My opinion is that if shelve is that poorly debugged, it's probably
not ready for prime time.

Or you could submit a bug report...

-- 
Bob Miller                              K<bob>
                                        kbob at jogger-egg.com