Importing anydbm generates exception if _bsddb unavailable

[vargish]

BPO	731501
Nosy	@loewis, @freddrake, @smontanaro
Files	bsddb185.diff

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = 'https://github.com/smontanaro'
closed_at = <Date 2005-05-23.01:38:01.000>
created_at = <Date 2003-05-02.17:56:07.000>
labels = ['library']
title = 'Importing anydbm generates exception if _bsddb unavailable'
updated_at = <Date 2005-05-23.01:38:01.000>
user = 'https://bugs.python.org/vargish'

bugs.python.org fields:

activity = <Date 2005-05-23.01:38:01.000>
actor = 'skip.montanaro'
assignee = 'skip.montanaro'
closed = True
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2003-05-02.17:56:07.000>
creator = 'vargish'
dependencies = []
files = ['871']
hgrepos = []
issue_num = 731501
keywords = []
message_count = 8.0
messages = ['15823', '15824', '15825', '15826', '15827', '15828', '15829', '15830']
nosy_count = 4.0
nosy_names = ['loewis', 'fdrake', 'skip.montanaro', 'vargish']
pr_nums = []
priority = 'normal'
resolution = 'accepted'
stage = None
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue731501'
versions = ['Python 2.3']

[vargish]

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.

[loewis]

Logged In: YES
user_id=21627

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?

[smontanaro]

Logged In: YES
user_id=44345

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.

[loewis]

Logged In: YES
user_id=21627

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

[loewis]

Logged In: YES
user_id=21627

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).

[smontanaro]

Logged In: YES
user_id=44345

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.

[freddrake]

Logged In: YES
user_id=3066

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.

[smontanaro]

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user_id=44345

ancient history i just never closed