[ python-Bugs-731501 ] Importing anydbm generates exception if _bsddb unavailable

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Bugs item #731501, was opened at 2003-05-02 13:56
Message generated for change (Comment added) made by fdrake
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Category: Python Library
Group: Python 2.3
Status: Open
Resolution: Accepted
Priority: 5
Submitted By: Nick Vargish (vargish)
>Assigned to: Skip Montanaro (montanaro)
Summary: Importing anydbm generates exception if _bsddb unavailable

Initial Comment:
The anydbm module attempts to import the dbhash module,
which fails if there is no BSD DB module available.

Relevant portion of backtrace:

  File "/diska/netsite-docs/cgi-bin/waisdb2.py", line
124, in _getsystemsdbm
    dbsrc = anydbm.open(self.dbfile)
  File
"/usr/local/python-2.3b1/lib/python2.3/anydbm.py", line
82, in open
    mod = __import__(result)
  File
"/usr/local/python-2.3b1/lib/python2.3/dbhash.py", line
5, in ?
    import bsddb
  File
"/usr/local/python-2.3b1/lib/python2.3/bsddb/__init__.py",
line 40, in ?
    import _bsddb
ImportError: No module named _bsddb

Tests that explicitly use "import dbm" rather than
anydbm are successful on this system.


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>Comment By: Fred L. Drake, Jr. (fdrake)
Date: 2004-06-24 02:09

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The doc changes look mostly fine to me (and I've changed
what didn't; a small cosmetic nit).

I'm just amazed we're still spending time tweaking BSD DB; I
don't think that's ever "just worked" for me without digging
around for a version of the underlying library that worked
with Python.


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Comment By: Skip Montanaro (montanaro)
Date: 2003-05-06 16:54

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Assigned to Fred for doc review - I added a couple notes to libbsddb.tex
and libundoc.tex in lieu of actually creating a separate bsddb185 section
which I felt would have given people the mistaken idea that the module is
available for general use.  Still, I thought there should be some mention in
the docs.

Library detection probably needs a little tweakage as well.


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Comment By: Martin v. Löwis (loewis)
Date: 2003-05-05 17:55

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Actually, you probably need to check whether
/usr/lib/libdb.* is present, and link with that as well if
it is.

If you are uncertain whether this is the right library, I
see no way except to run a test program, at configure time,
that creates a database and determines whether this really
is a DB 1.85 database. Alternatively, the test program might
try to invoke db_version. If the function is available, it
is DB x, x>=2 (DB1 apparently has no version indication
function).

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Comment By: Martin v. Löwis (loewis)
Date: 2003-05-05 16:34

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I can't actually test the patch, but it looks good to me.
Please apply!

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Comment By: Skip Montanaro (montanaro)
Date: 2003-05-05 10:27

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I believe the attached patch does what's necessary to get this to work again.
It does a few things:
  * setup.py builds the bsddb185 under the right (restrictive) circumstances.
    /usr/include/db.h must exist and HASHVERSION must be 2.  In this case
    the bsddb185 module will be built without any extra includes, libraries
    or #defines, forcing whatever is present in /usr/include/db.h and libc to
    be used to build the module.

  * whichdb.py detects the older hash file format and returns "bsddb185".

  * bsddbmodule.c grows an extra undocumented attribute, "open".

The last two changes avoid having to change dbhash.py in complicated
ways to distinguish between new and old file versions.  The format-
detecting mess remains isolated to whichdb.py.

Using this setup I was successfully able to open /etc/pwd.db on my
system using anydbm.open(), which I was unable to do previously.  I can
also still open a more recent hash file created with anydbm.open.  Finally,
new files created with anydbm.open are in the later format.

Please give it a try.


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Comment By: Martin v. Löwis (loewis)
Date: 2003-05-03 05:02

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I think this is not a bug. open() has determined that this
is a bsddb file, but bsddb is not supported on the system.

Or did you mean to suggest that opening the very same file
with dbm would be successful?

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