Shelve problem in 1.5.2

[Skip Montanaro]

    Nick> I have just upgraded from 1.5.1 to 1.5.2 on a Linux/RedHat(now
    Nick> 6.1) system and my shelve module is behaving strangely. It fails
    Nick> to open old files and if I open and close a new file it is happy
    Nick> but as soon as I try to open the newly created file it fails
    Nick> also...

Nick,

Try the attached version of whichdb.py to see if it cures your ills.

Skip Montanaro | http://www.mojam.com/
skip at mojam.com | http://www.musi-cal.com/
847-971-7098   | Python: Programming the way Guido indented...

--[[application/octet-stream
Content-Disposition: attachment; filename="whichdb.py"][quoted-printable]]
"""Guess which db package to use to open a db file."""

import struct

def whichdb(filename):
    """Guess which db package to use to open a db file.

    Return values:

    - None if the database file can't be read;
    - empty string if the file can be read but can't be recognized
    - the module name (e.g. "dbm" or "gdbm") if recognized.

    Importing the given module may still fail, and opening the
    database using that module may still fail.
    """

    # Check for dbm first -- this has a .pag and a .dir file
    try:
        f =3D open(filename + ".pag", "rb")
        f.close()
        f =3D open(filename + ".dir", "rb")
        f.close()
        return "dbm"
    except IOError:
        pass

    # See if the file exists, return None if not
    try:
        f =3D open(filename, "rb")
    except IOError:
        return None

    # Read the start of the file -- the magic number
    s16 =3D f.read(16)
    f.close()
    s =3D s16[0:4]

    # Return "" if not at least 4 bytes
    if len(s) !=3D 4:
        return ""

    # Convert to 4-byte int in native byte order -- return "" if impossib=
le
    try:
        (magic,) =3D struct.unpack("=3Dl", s)
    except struct.error:
        return ""

    # Check for GNU dbm
    if magic =3D=3D 0x13579ace:
        return "gdbm"

    # Check for BSD hash
    if magic in (0x00061561, 0x61150600):
        return "dbhash"

    # BSD hash v2 has a 12-byte NULL pad in front of the file type
    try:
	(magic,) =3D struct.unpack("=3Dl", s16[-4:])
    except struct.error:
        return ""

    # Check for BSD hash
    if magic in (0x00061561, 0x61150600):
        return "dbhash"

    # Unknown
    return ""